> For the complete documentation index, see [llms.txt](https://gzqsjtu.gitbook.io/workspace/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://gzqsjtu.gitbook.io/workspace/javascript/function-api.md). # function API Array, String, Object ## Array
InPlace:push()/pop(), shift()/unshift(), **splice(),** copyWithin(), fill(), reverse(), sort()
ReturnNew: concat(), slice()\ `***`**splice(), splice(startIndex, deleteNumber, input new to here);** ``` array.splice(start[, deleteCount[, item1[, item2[, ...]]]]) ``` Matching: indexOf(), lastIndexOf(), find(), findIndex(), some(), every(), join()ty #### Empty the Array var arr = \[1] 1. arr.splice(0, arr.length); 2. arr.length = 0; 3. arr = \[] **traverse forEach** executes the provided callback once for each element present in the array in ascending order. ``` fruits.forEach(function (item, index, array) { console.log(item, index); }); ``` •Does not make a copy of the array before iterating. ``` split var myArray = myData.split(','); var myNewString = myArray.join(','); myNewString; ``` push(): add to last. pop(): delete last and return this one. [`toString()`](https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/toString) 1. ``` var dogNames = ["Rocket","Flash","Bella","Slugger"]; dogNames.toString(); //Rocket,Flash,Bella,Slugger ``` ``` var myArray = ['Manchester', 'Leeds', 'Carlisle']; myArray.push('Cardiff'); myArray.pop(); pop() delete last one var removedItem = myArray.pop(); ``` [`unshift()`](https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/unshift) [`shift()`](https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/shift) `100% like push and pop, only on the begining` `unshift(): add to head.` ``` myArray.unshift('Edinburgh'); var removedItem = myArray.shift(); ``` ``` .indexOf(element) return the index ``` Splice: delete some elements: ``` array.splice(start[, deleteCount[, item1[, item2[, ...]]]]) start position, delete number, items to add.from start return the [] that deleted. ``` ``` var removedItem = fruits.splice(pos, 1); ``` .fill() fill all indexes. [`.concat()`](https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/concat) [`Array.prototype.includes()`](https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/includes) [`Array.prototype.join()`](https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/join) `concat and return a new String` join(" + ") use " + " to concat [`Array.prototype.slice()`](https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/slice) `get some return a new array` ``` arr.slice(begin, end); // [begin, end) ``` [`Array.prototype.toString()`](https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/toString) [`Array.prototype.lastIndexOf()`](https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/lastIndexOf) `return the last index..` Traverse: [`Array.prototype.forEach()`](https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach) [`Array.prototype.map()`](https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/map) ![](https://4116032991-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LgnugJ0SdX2tMAwP37V%2F-Li6lCc1yK8BklAkdxk2%2F-Li6lDIjLkob_ZyGL7MN%2Fimage.png?alt=media\&token=0113e6cb-2266-4de0-9504-eb8b5d0b0148) [`Array.prototype.reduce()`](https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce) let finalVal = oldArray.reduce((accumulator, currentValue, currentIndex, array) => { ... }), initalValue; ![](https://4116032991-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LgnugJ0SdX2tMAwP37V%2F-Li6lCc1yK8BklAkdxk2%2F-Li6l_4PSuL5t8x5vTMJ%2Fimage.png?alt=media\&token=a4684f5a-dfbb-4233-bd49-4852e98dd7bc) [`Array.prototype.some()`](https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/some) `as least one or return false;` [`Array.prototype.filter()`](https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/some) ![](https://4116032991-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LgnugJ0SdX2tMAwP37V%2F-Li6lCc1yK8BklAkdxk2%2F-Li6lNmp7bnfIEJ82q6P%2Fimage.png?alt=media\&token=3b00c2c1-bcf3-4194-ac9b-94068b49424d) ## Object •**map** transforms the elements in the array •Based on a function you give •Return a copy and doesn’t modify the input array •When the function you provide gets called, it gets called for each element with three arguments: the element itself, the index of the element, and the array itself (which is seldom useful). •**filter** removes unwanted things from an input array. •Based on a function you give •Return a copy and doesn’t modify the input array •map and filter often are used together [`Object.assign()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign)Copies the values of all enumerable own properties from one or more source objects to a target object. [`Object.keys()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys)Returns an array containing the names of all of the given object's **own** enumerable string properties. [`Object.values()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/values)Returns an array containing the values that correspond to all of a given object's **own** enumerable string properties. ### Reduce() array.reduce((accumulator, currentValue, currentIndex, sourceArray) => { }) ``` arr.reduce(callback(accumulator, currentValue[, index[, array]])[, initialValue]) ``` ## For Loop: for（x of Array） {// } arrays strings maps nodelists etc but loop an object: we use in. for (x in Object){ // } While loop / do while loop ## String Strings can also be created using the `String` global object directly: ``` String(thing) new String(thing) ``` #### [Character acces](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String#Character_access)s string.[`charAt()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/charAt) ``` return 'cat'[1]; ``` ### [`String` instance](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String#String_instances) `String.prototype.constructor`Specifies the function that creates an object's prototype.[`String.prototype.length`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/length)Reflects the length of the string. ### [`String.prototype.concat()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/concat)Combines the text of two strings and returns a new string. ### [`String.prototype.includes()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/includes)Determines whether one string may be found within another string. [`String.prototype.indexOf()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/indexOf)Returns the index within the calling [`String`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String) object of the first occurrence of the specified value, or -1 if not found. [`String.prototype.lastIndexOf()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/lastIndexOf)Returns the index within the calling [`String`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String) object of the last occurrence of the specified value, or -1 if not found. [`String.prototype.match()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/match)Used to match a regular expression against a string.[`String.prototype.matchAll()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/matchAll)Returns an iterator of all matches.[`String.prototype.normalize()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/normalize)Returns the Unicode Normalization Form of the calling string value. [`String.prototype.repeat()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/repeat)Returns a string consisting of the elements of the object repeated the given times. ### [`String.prototype.replace()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replace)Used to find a match between a regular expression and a string, and to replace the matched substring with a new substring. [`String.prototype.search()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/search)Executes the search for a match between a regular expression and a specified string. ### [`String.prototype.slice()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/slice)Extracts a section of a string and returns a new string. ``` str.slice(beginIndex[, endIndex]) ``` ### [`String.prototype.split()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/split)Splits a [`String`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String) object into an array of strings by separating the string into substrings. ``` str.split([separator[, limit]]) ``` ### [`String.prototype.substring()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/substring)Returns the characters in a string between two indexes into the string. [`String.prototype.toLowerCase()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/toLowerCase)Returns the calling string value converted to lower case. [`String.prototype.toUpperCase()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/toUpperCase)Returns the calling string value converted to uppercase. str.split("dog").join("cat"); ### [`String.prototype.toString()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/toString)Returns a string representing the specified object. Overrides the [`Object.prototype.toString()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/toString) method. ### Methods[Section](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String#Methods) [`String.fromCharCode()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/fromCharCode)Returns a string created by using the specified sequence of Unicode values.[`String.fromCodePoint()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/fromCodePoint)Returns a string created by using the specified sequence of code points.[`String.raw()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/raw) Returns a string created from a raw template string. ## typeof **typeof null = objec** | **Type** | result | | -------------------------------- | -------------------------- | | Null | `"object"`（见下文） | | Boolean | `"boolean"` | | Number | `"number"` | | String | `"string"` | | Symbol （ECMAScript 6 新增） | `"symbol"` | | 宿主对象（由JS环境提供） | *Implementation-dependent* | | 函数对象（\[\[Call]] 在ECMA-262条款中实现了） | `"function"` | | 任何其他对象 | `"object"` | New ``` var str = new String('String'); var num = new Number(100); typeof str; // It will return 'object' typeof num; // It will return 'object' ``` Float parseFloat(String s) return float ## JSON JSON.stringify() Convert a JavaScript object into a string JSON.parse() Convert text into a JavaScript object: