Js string indexof indexOf (searchValue [, fromIndex]) indexOf 方法接受兩個參數，第一個參數為欲搜尋的字串，第二個參數為開始查找的位置，默認值為 0。 JavaScript String indexOf () indexOf () 方法用來判斷字串 字串 變數中是否包含某字串。 語法： str. JavaScript indexOf method return index position of the first occurrence of a given string. The W3Schools online code editor allows you to edit code and view the result in your browser Nov 2, 2023 · The indexOf() method and the includes() method in JavaScript are both used for searching within a string to check for the existence of… String. Dec 9, 2008 · If your situation requires the use of a regular expression, use the search() method, otherwise; the indexOf() method is more performant. Sep 19, 2013 · Javascript's String. The JavaScript string indexOf method is a powerful and efficient way to search inside strings and is commonly used in text processing, filtering, and Mar 1, 2024 · The String. If it is not found, JavaScript indexof return -1. But you have to make sure to check with same Jul 9, 2020 · The indexOf () method checks if an array includes passed element or not. Jan 1, 2022 · The indexOf function of a string does not return a character but rather returns the position of the first place that string or character is found, not the character itself. The lastIndexOf() method searches the string from the end to the beginning. test('foo') because both result in a bool value. The method returns a 0-based index, making it a fundamental JavaScript string manipulation way. Jul 10, 2025 · Description Strings are useful for holding data that can be represented in text form. Using includes() method. Searching for a Single Character The indexOf() method can also be used to search for a single character in a string. The indexOf() method returns the index within the calling String object of the first occurrence of the specified value, starting the search at fromIndex. 说明 String. ) take into account the value of an array's length Sep 28, 2024 · The IndexOf method is a built-in function in JavaScript that returns the position of the first occurrence of a specified substring within a string. I'm looking for the starting position of nth occurrence, in this case the second. This tutorial shows you how to use the JavaScript Array indexOf() method to find the first index of the element. # Split a String at multiple indices using JavaScript If you need to split a string at multiple indices, use this approach instead. This method turns the string into an upper case string. The lastIndexOf() method returns -1 if the value is not found. indexOf() case insensitive. Still, setting "string indexes" on an Array object is not using the array characteristics of the Array object. The test cases cover various scenarios, including searching for a specific substring at the start or end of a string. May 21, 2019 · I'm trying to some string manipulation using javascript/jquery. Sorry for confusion I'm not looking for the last index. So in order to check if your variable starts with "1|Accept" you should check if indexOf returns 0. The lastIndexOf() method returns the index from the beginning (position 0).  The includes() method check if an array includes a certain element, returning true or false as appropriate. Apr 4, 2025 · JavaScript indexOf tutorial shows how to find elements in JavaScript arrays and strings. indexOf("good")); Jul 13, 2014 · You can't make . Examples Find the index of string: I like Pablo's answer, but Array#indexOf and Array#map don't work on all browsers. JavaScript String indexOf method: Syntax, Usage, and Examples The indexOf() method in JavaScript allows you to find the position of a substring within a string. The substring() method extracts characters, between two indices (positions), from a string, and returns the substring. The indexOf() method is case sensitive. Does indexOf () work with strings, array, etc? Yes, indexOf() works with array (of number, string, or any object), as well as with string. The indexOf() method starts at a specified index and searches from left to right (from the given start postion to the end of the array). Sep 9, 2019 · Learn how to use String. 5w次，点赞15次，收藏29次。本文详细介绍了JavaScript中String类型的indexOf方法，包括其功能、区分大小写特性以及与Number类型和Array类型的区别。特别提到indexOf方法不会进行隐式类型转换，并强调了严格等于的使用规则。 Sep 28, 2025 · Only years['2'] is an actual array index. Jul 20, 2025 · The findIndex() method of Array instances returns the index of the first element in an array that satisfies the provided testing function. indexOf() 方法从头到尾检索字符串 string，看它是否包含子串 substring。 开始检索的位置在字符串 string 的 start 处或 string 的开头（没有指定 start 参数时）。 如果找到了一个 substring，那么 String. Additionally, you can specify an index, defined by num in the syntax definition, to start your search for the string specified. An array is an ordered list of values that you refer to with a name and an index. Perfect for beginners. ' within the string '123. But in ES5 we are used to performing operations like this with indexOf() method. For more complex requirements a regular expression pattern and search() can be used. Tip: Use the lastIndexOf method to return the position of the last occurrence of specified character (s) in a string. The index of the first character is 0, the second 1, May 21, 2012 · From MDN: string. By default the search starts at the first element and ends at the last. Because "100" string is not same as 100 number. and the search strin Dec 12, 2024 · JavaScript provides several methods to work with strings efficiently, enabling you to implement search features in your applications seamlessly. May 8, 2020 · The JavaScript indexOf method allows programmers to find out whether a string or array contains a value, and returns the index number at which that value starts. indexOf () to find one or more matching string patters within a given string? For example: I have a string to test: /accounts/ {account}/project/ {project} I want to te Learn how to use the indexOf function in JavaScript to find the index of a string or substring within a string. Jan 30, 2023 · The indexOf() method is a built-in JavaScript method that returns the first incidence of the string in the string calling the method. It returns the index of the first occurrence or -1 if the substring doesn’t exist. years['02'] is an arbitrary string property that will not be visited in array iteration. That said, for simple expressions without groups and anchors the performance should be comparable. Several of the built-in array methods (e. 定义和用法 indexOf () 方法可返回某个指定的字符串值在字符串中首次出现的位置。 如果没有找到匹配的字符串则返回 -1。 注意： indexOf () 方法区分大小写。 提示： 同样你可以查看类似方法 lastIndexOf () 。 Nov 13, 2024 · The indexOf() function in JavaScript is a versatile tool for identifying the position of characters or substratches within strings. In JavaScript, indexOf () is a string method that is used to find the location of a substring in a string. If you only have to split the string based on a provided index once or twice, it's better to avoid premature abstractions. Definition and Usage The indexOf() method returns the position of the first occurrence of specified character (s) in a string. Creating strings Strings can be The W3Schools online code editor allows you to edit code and view the result in your browser Jul 10, 2025 · The substring() method of String values returns the part of this string from the start index up to and excluding the end index, or to the end of the string if no end index is supplied. W3Schools offers free online tutorials, references and exercises in all the major languages of the web. と数え上げるので、最初の文字で見つかった場合は 0 が返ってくる。これを利用して前方一致の判定を実現できる。 前方一致のコードを短縮する Jun 23, 2021 · Syntax string. This includes arrays and array-like constructs such as Array objects and TypedArray objects. Mar 4, 2024 · A step-by-step guide on how to insert a string at a specific index of another string in JavaScript. While searching a string, includes accepts regexpes as opposed to indexOf Readability arr. indexOf(searchValue[, fromIndex]) searchValue 是你要搜尋的字串 fromIndex 從哪個位置開始找起，預設為 0 返回找到的位置，第一個位置從 0 開始算起；找不到則返回 -1 用法： Jul 23, 2025 · Using String lastIndexOf () Method The lastIndexOf() method finds the index of the last occurrence of a specific character in a string. indexOf是會區分大小寫的。 Dec 19, 2022 · The indexOf method is a widely used tool in JavaScript for finding the position of a specified value within an array or a string. Let's search for the first occurrence of the character 'a' in a string. Learn about how to use the indexOf method on Career Karma. indexOf () method returns the index of the first occurrence of a substring in a string. Jul 8, 2025 · Indexed collections Previous Next This chapter introduces collections of data which are ordered by an index value. The lastIndexOf() method is case sensitive. The indexOf() method returns -1 if the value is not found. Question: How do I locate the position of a given character in a string variable? Answer: To determine the position of a given character c (or a given substring c) within a string, use the JavaScript string. Aug 22, 2020 · str. g. Then, use . Basic String Methods Javascript strings are primitive and immutable: All string methods produce a new string without altering the original string. nds=[100,200] which is true. Aug 29, 2020 · The indexOf() method is useful for determining the index at which a string starts at, if that string is contained inside another string. 4567', this can be accomplished with Aug 19, 2022 · The indexOf method returns the index within the calling string object of the first occurrence of the specified value, starting the search at startIndex. The function accepts a string and the character to find as parameters. The provided benchmark is designed to compare the performance of different string manipulation methods: Regular Expressions (Regex), startsWith, and indexOf. indexOf() は String 値のメソッドで、この文字列を検索し、指定した部分文字列が最初に出現するインデックスを返します。 オプションで開始位置を取り、指定した数値以上のインデックスで指定した部分文字列が最初に出現するインデックスを返します。 Jan 30, 2013 · 在jjavascript中，String. indexOf() method to check if a string contains a substring in JavaScript. This method is the same as the String. indexOf() using RAL instead of Ral. indexOf() method, like this: pos = string. indexOf('bar') !== -1 is better comparable to /bar/. It offers a user-friendly but limited functionality, similar to JavaScript's pattern-matching regular expressions (the RegExp object, covered in later tutorials). One such method is indexOf (), which is used to locate a substring within another string and Apr 3, 2024 · 文章浏览阅读2. # Using the length of the replacement string to determine the start index If you need to replace multiple characters in the string with multiple characters, use the length of the replacement string to determine the first String 的 indexOf() 方法在字符串中搜索指定子字符串，并返回其第一次出现的位置索引。它可以接受一个可选的参数指定搜索的起始位置，如果找到了指定的子字符串，则返回的位置索引大于或等于指定的数字。 In this tutorial, we will learn about the JavaScript String indexOf () method with the help of examples. lastIndexOf () method, but it starts at the beginning of the string. The JavaScript String indexOf () method is used to find the index of the first occurrence of the specified substring in the original string. var noPic = largeSrc. I'm trying to find the positions of all occurrences of a string in another string, case-insensitive. Sep 30, 2024 · The indexOf () method in JavaScript is used to find the index of the first occurrence of a specified value within a string. The indexOf () method of an instance of the String object returns the indexed start position of the string passed. Covering popular subjects like HTML, CSS, JavaScript, Python, SQL, Java, and many, many more. indexOf(" Oct 1, 2025 · The lastIndexOf() method of String values searches this string and returns the index of the last occurrence of the specified substring. I have created a indexof function in but it is not giving the correct output: Question is: /* Implement a function called indexOf that accepts two parameters: a string and a Aug 28, 2019 · Curious about JavaScript indexOf vs includes performance on a string ? Let's dive in and see if one method is faster than the other. g "100", was not found in an array of numbers, e. Jul 10, 2025 · The charAt() method of String values returns a new string consisting of the single UTF-16 code unit at the given index. It returns the index of where the string is first found, from the beginning of the search string. 6w次，点赞27次，收藏55次。本文详细介绍了JavaScript中常用的字符串操作方法，包括indexOf ()方法用于查找指定字符串首次出现的位置、split ()方法用于分隔字符串生成数组、join ()方法用于连接数组元素成字符串及replace ()方法用于替换字符串内容等。 The W3Schools online code editor allows you to edit code and view the result in your browser It returned -1 when el string, e. toUpperCase() after referrer. includes('searchedElement') does what it says and it is obvious that it returns a boolean. The at() method returns the same as []. Description The indexOf() method returns the position of the first occurrence of a value in a string. indexOf("nopic"); Should I write : var noPic = largeSrc. example: ' Jul 7, 2025 · Learn how to use indexOf() in JavaScript with syntax, examples, use cases, and best practices for arrays and strings. while arr. Dec 21, 2011 · I am learning Javascript and don't understand why the indexOf below returns -1: var string = "The quick brown fox jumps over the lazy dog"; console. Some of the most-used operations on strings are to check their length, to build and concatenate them using the + and += string operators, checking for the existence or location of substrings with the indexOf() method, or extracting substrings with the substring() method. toLowerCase(). indexOf ()方法是用來搜索， 並傳回指定子字串在字串中第一次出現的位置 ( 由左至右 )，位置是由0開始計算。 除了可以從字串頭開始尋找外，也可以指定開始搜索的起始位置。 如果找不到指定字串會傳回-1。 要注意一點！String. Actually String. indexOf() supports second param, fromIndex (doc). JavaScript String indexOf () The indexOf() method returns the index (position) of the first occurrence of a string in a string, or it returns -1 if the string is not found: Description The at() method returns an indexed character from a string. If the index is greater than or equal to the array's length, -1 is returned, which means the array will not be searched. Sep 8, 2017 · indexOf JavaScript method explained: learn how to easily use indexOf JavaScript method in your projects. Jul 13, 2017 · The indexOf () method returns the index within the calling String object of the first occurrence of the specified value, starting the search at fromIndex. Aug 16, 2019 · How can I use String. Mar 4, 2024 · The code sample achieves the same result but is a bit more hardcoded and simplified. It takes an optional starting position and returns the first occurrence of the specified substring at an index greater than or equal to the specified number. indexOf(c); For example, if you want to find the position of the character '1' or '. Each character in a JavaScript string can be accessed by an index number, and all strings have methods and properties available to them. Underscore will use native code if it's available, but has fallbacks as well. startSearch (optional), indicates the index to start the search at. You could do . The indexOf() method of String values searches this string and returns the index of the first occurrence of the specified substring. indexOf(value, startSearch); value is the value to search for in a string. Oct 2, 2012 · Add . In Node. fromIndex The index to start the search at. This JavaScript tutorial explains how to use the string method called indexOf () with syntax and examples. IndexOf example This method searches strings—we pass it a substring we want to find in a I am trying to find if an image has in its source name noPic which can be in upper or lower case. You can normalize the case between the Array and the search term. Another method, includes, also can search for strings. Jul 10, 2025 · The indexOf() method of Array instances returns the first index at which a given element can be found in the array, or -1 if it is not present. If the substring is not found, it returns -1. indexOf returns the index of the a search term within a string. For example, given the string: I learned to play the Ukulele in Lebanon. If the provided index value is a negative number, it is taken as the offset from the end of the array. If the string that is passed as a parameter to the indexOf()… 2 You can use the fromIndex of Array#indexOf. Jul 12, 2025 · These are the following methods to insert a string at a specific index in JavaScript: 1. In this article, you will learn about the indexOf () method of String with the help of examples. . Feb 5, 2025 · A comprehensive guide to the JavaScript String indexOf() method, explaining how to find the index of a substring within a string. It takes an optional starting position and returns the last occurrence of the specified substring at an index less than or equal to the specified number. Sep 29, 2025 · 文章浏览阅读4. match is wasting doing too Dec 16, 2019 · An overview of how the indexOf() method works to find the position of a substring in a string or an item in an array in Javascript. indexOf() 将返回 substring 的第一个字符在 string 中的位置。 JavaScript String indexOf () The indexOf() method returns the index (position) of the first occurrence of a string in a string, or it returns -1 if the string is not found: Aug 24, 2021 · Introduction A string is a sequence of one or more characters that may consist of letters, numbers, or symbols. How do I find the position of a substring within a string starting at a position somewhere in the middle of the string?. If the substring is not contained in the string, the method returns -1. log (string. For example, Well yes, that goes back to the fact that virtually everything in Javascript is an object is a function is an object and the . Jul 10, 2025 · The indexOf() method of String values searches this string and returns the index of the first occurrence of the specified substring. It returns the position of the substring, or -1 if the substring is not present. js, we can search a string with indexOf or lastIndexOf —an index integer is returned. Jun 6, 2023 · In this example, we search for "javascript" (with a lowercase 'j'), and the indexOf() method returns -1, indicating that the specified value was not found in the string. The indexOf () method allows you to retrieve the position index of the first instance of a substring in a given string. In this tutorial, you'll learn how to use the JavaScript String indexOf() method to find the index of a substring within a string. It works similarly to indexOf() but searches from the end of the string. The boolean expression 'foo'. 2 Here is a short solution using a function expression (with ES6 arrow functions). Performances Is there a way to retrieve the (starting) character positions inside a string of the results of a regex match() in Javascript? Inserting at a specific index (rather than, say, at the first space character) has to use string slicing/substring: I have a string, let's say Hello world, and I need to replace the char at index 3. By returning a numeric index or -1 when not found, it provides a robust way to handle string search operations efficiently. If no elements satisfy the testing function, -1 is returned. Jul 10, 2025 · The slice() method of String values extracts a section of this string and returns it as a new string, without modifying the original string. , join(), slice(), indexOf(), etc. notation and the [] notation of accessing object properties are all the same really. In this tutorial, we will learn the difference between string primitives and the String object, how strings are indexed, how to access characters This tutorial explains the indexOf () method, part of the JavaScript String object. The new string is then placed between these slices, effectively inserting it at the desired index. prototype. Using the slice () Method Inserting a string using the slice () method involves splitting the original string into two parts: one before the insertion point and one after. The indexOf() method returns the first index (position) of a specified value. You seem to be doing a search and then converting the case, so that isn't going to help you. The tutorial provides numerous examples to demonstrate element searching in JS. But the difference is The indexOf () method returns position, it returns -1 if an element is not found. search because both will return the start index of the match. It splits the string into an array of characters and uses a reduce function to accumulate and return the matching indices as an array. Jul 8, 2025 · Learn how to use indexOf() in JavaScript with syntax, examples, best practices, and comparisons with includes(). indexOf(searchValue[, fromIndex]) Returns the index within the calling String object of the first occurrence of the specified value, starting the search at fromIndex, returns -1 if the value is not found. Relationship between length and numerical properties A JavaScript array's length property and numerical properties are connected. Description The lastIndexOf() method returns the index (position) of the last occurrence of a specified value in a string. The substring() method extracts characters from start to end (exclusive). toUpperCase() on the dnameVal before the search, but that would only work if all the names are also upper case. Dec 27, 2023 · IndexOf Suppose one string exists as a substring inside another. indexOf('searchedElement') !== -1 to know if something exists in a string or an array is less more readable. Sep 22, 2017 · 解説 indexOf() はターゲット文字列内の何文字目でパターン文字列が見つかったのか返す。 0文字目,1文字目,. How can I replaced a char by specifying an index? var str = "hello world"; I need something like str. I am new to JavaScript. Description The charAt() method returns the character at a specified index (position) in a string. JavaScript string indexOf examples included. indexOf is more comparable to String. For example, consider an array called emp, which contains employees' names indexed by their numerical Sep 4, 2017 · ES2016 Specifications included the includes() method for Array data structure. str. If you store the result of the first indexOf, just reuse it. Returns -1 if the value is not found. fcxdgi bvfqr emaqiq wvyis fgi toxc yusq vobci ffdnd gcgzme nnffp zkrtx xzcsi namvos hcawj