username = "Violator"; // not a valid variable var 1user_name = "Violator"; // not a valid variable var user_name = "Violator"; // valid variable var userName = "Violator"; // valid variable var username = "Violator"; // valid variable Listing 3-1Valid and Invalid Ways to Creat...
function greet(name) { return `Hello, ${name}!`; } 数据类型检查和转换 在JavaScript中,你可以使用typeof操作符来检查变量的数据类型。对于更复杂的类型判断,Array.isArray()或者instanceof操作符通常更为适用。 typeof 'Hello'; // "string" typeof 10; // "number" typeof true; // "boolean" ty...
}// create function objects for each type of coffeevarcolumbian =function(){this.name='columbian';this.basePrice=5; };varfrenchRoast =function(){this.name='french roast';this.basePrice=8; };vardecaf =function(){this.name='decaf';this.basePrice=6; };// create object literals for the ...
// here we are in global scope var globalVariable = 'xyz'; function f() { var localVariable = true; function g() { var anotherLocalVariable = 123; // All variables of surround scopes are accessible localVariable = false; globalVariable = 'abc'; } } // here we are again in global...
foo=4;// change variable `foo` 复制 复合赋值运算符 有复合赋值运算符,比如+=。以下两个赋值是等价的: x+=1;x=x+1; 复制 标识符和变量名 标识符是在 JavaScript 中扮演各种语法角色的名称。例如,变量的名称是标识符。标识符区分大小写。 大致而言,标识符的第一个字符可以是任何 Unicode 字母、美元符号...
functionlogName(name){varn = name ||"Mark";console.log(n);} logName();// "Mark" 3. undefined 和 null 有什么区别? 在了解 undefined 和 null 的区别之前,我们先来看看它们的相同点。 它们都属于 JavaScript 中的 7 种基本类型。 letprimitiveTypes = ...
If you put a number in quotes, it will be treated as a text string. Example constpi =3.14; letperson ="John Doe"; letanswer ='Yes I am!'; Try it Yourself » Declaring a JavaScript Variable Creating a variable in JavaScript is called "declaring" a variable. ...
Create an Array from a String: Array.from("ABCDEFG")// Returns [A,B,C,D,E,F,G] Try it Yourself » Array keys() Thekeys()method returns an Array Iterator object with the keys of an array. Example Create an Array Iterator object, containing the keys of the array: ...
Prevents accidental globals.Without strict mode, assigning a value to an undeclared variable automatically creates a global variable with that name. This is one of the most common JavaScript errors. In strict mode, attempting to do so throws an error. ...
reporter {string|constructor}You can pass a reporter's name or a custom reporter's constructor. You can find recommended reporters for the browser here. It is possible to use built-in reporters as well. Their employment in browsers is neither recommended nor supported, open the console to see...