javascript中对灵活的类型抓换规则对“判断相等”(equality) javascript的变量是无类型的(untyped),变量可以被赋予人和类型的值,使用var关键字来声明(declare)变量。javascript采用语法作用域,不在任何函数内声明的变量称为全局变量(global variable),它在javascript的程序 中任何地方都是可见的。 1.数字 和其它编程语言...
在javascript中,使用一个变量之前应当先声明(declare),变量是使用关键字var(variable的缩写)来声明的 vari;varsum; 也可以通过一个var关键字来声明多个变量 vari ,sum; 赋值 把值存入变量的操作称为赋值(assignment)。一个变量被赋值以后,我们就说该变量包含这个值 给变量第一次赋值的过程,叫初始化 我们可以将变量...
三十一、Access Multi-Dimensional Arrays With Indexes 用索引访问多维数组 letourArray=[["a",50],["b",60],["c",70]]console.log(ourArray[1][1]);结果:60 三十二、Manipulate Arrays with .push()用.push()增尾操作数组 letourArray=[["a",50],["b",60],["c",70]];ourArray.push(["d"...
ourArray[0] = 1; // ourArray等于 [1,2,1] 任务 修改数组myArray中索引0上的值为3。 // 举例 var ourArray = [1,2,3]; ourArray[1] = 3; // ourArray now equals [1,3,3]. // Setup var myArray = [1,2,3]; // Only change code below this line. myArray[0]=3; JavaScript ...
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 Data types Explained ...
Using an array literal is the easiest way to create a JavaScript Array.Syntax: const array_name = [item1, item2, ...]; It is a common practice to declare arrays with the const keyword. Learn more about const with arrays in the chapter: JS Array Const....
JavaScript 有两种注释:单行注释和多行注释。单行注释以//开头,并在行尾终止: x++;// single-line comment 复制 多行注释由/*和*/界定: /* This is a multiline comment. */ 复制 变量和赋值 在JavaScript 中,变量在使用之前被声明: varfoo;// declare variable `foo` ...
In the following statements, the variable x is not assigned a value, and the if statement evaluates to true. varx;if(x===undefined){dosomething;}else{dosomething;} Variables Usage: The variables can be declared and used in two ways locally and globally. When you declare a JavaScript varia...
let:Declares a block-scoped(块作用域), local variable(局部变量), optionally initializing it to a value. const:Declares a block-scoped, read-only named constant(只读命名常量). With the keyword var. For example, var x = 42. This syntax can be used to declare both local and global variabl...
When assigning a variable to an object property, if the variable name is equal to the property name, you can do the following:const x = 10; const myObj = { x }; console.log(myObj.x) // 10ExplanationUsually (pre-ES2015) when you declare a new object literal and want to use ...