varcolors =newArray();//create an arrayvarcount = colors.unshift("red", "green");//push two itemsalert(count);//2count= colors.unshift("black");//push another item onalert(count);//3varitem = colors.pop();//get the first itemalert(item);//"green"alert(colors.length);//2 12...
arr2[0] = 'first element'; console.log(arr2); // ["first element"]vararr3 =Object.create(Array.prototype); arr3[0] = 'first element'console.log(arr3); // Array {0: "first element"} 以上代码可以看出用Object.create创建的数组返回的是Object, 如果把arr3[0] = 'first element'换成a...
JavaScript new Array() JavaScript has a built-in array constructornew Array(). But you can safely use[]instead. These two different statements both create a new empty array named points: constpoints =newArray(); constpoints = [];
>typeoftrue'boolean'>typeof'abc''string'>typeof{}// empty object literal'object'>typeof[]
Write a JavaScript function to find an array containing a specific element. Test data : arr = [2, 5, 9, 6]; console.log(contains(arr, 5)); [True] Click me to see the solution 33. Empty Array Write a JavaScript script to empty an array while keeping the original. ...
随着let和const这两个关键字的添加,JS增加了块级作用域的概念。 如何在JavaScript中使用let 当我们在用let声明变量时,用于声明一次之后就不能再以相同的名称重新声明它。 代码语言:javascript 代码运行次数:0 运行 AI代码解释 // ES5 Codevarvalue=10;console.log(value);// 10varvalue="hello";console.log(valu...
{// 'unused' is the only place where 'priorThing' is referenced,// but 'unused' never gets invokedif(priorThing) {console.log("hi"); } }; theThing = {longStr:newArray(1000000).join('*'),// Create a 1MB objectsomeMethod:function() {console.log(someMessage); } }; };setInterval...
constarray= [1,2,3,4]constindex =array.findIndex((num) => num >2)// 2constlastIndex =array.findLastIndex((num) => num >2)// 3 4.WeakMap支持使用Symbol作为key 很久以前,我们只能使用一个对象作为 WeakMap 的key。 constw...
Declare (create) stringsDeclare (create) numbersDeclare (create) an arrayDeclare (create) an objectFind the type of a variableAdding two numbers and a stringAdding a string and two numbersAn undefined variableAn empty variable JavaScript Objects ...
Array.from()可以基于给定的参数创建一个新数组,而map()可以处理数组的每个元素。 // 写法一: function create2DArray(m, n) { return Array.from({ length: m }, () => Array.from({ length: n }, () => 0)); } // 写法二: function create2DArray(m, n) { ...