题主所说的代码形式就是为了在语言层面不支持默认参数（default parameter）功能时的变通做法。正因为它的...
Sometimes this is acceptable, but sometimes it is better to assign a default value to the parameter: Example functionmyFunction(x, y) { if(y === undefined) { y =2; } } Try it Yourself » Default Parameter Values ES6allows function parameters to have default values. ...
#Using Default Value as Function Parameter Quite often you would see||being used like this: function(name){name=name||'no name';} Note: this is not the recommended way anymore. It's way better to ES6's default parameters. Because quite often, you might not want the default to kick in...
Default Parameter Values ES6 allows function parameters to have default values. Example functionmyFunction(x, y =10) { // y is 10 if not passed or undefined returnx + y; } myFunction(5);// will return 15 Try it Yourself »
Function如果运行时环境正在解析一个函数对象,那么这个值就为那个函数对象。如果正在解析一个脚本(script)或者模块(module),那么这个值为null Realm(域)来自相关代码可以访问的ECMAScript resources的域。注:ECMAScript resources包含客户端ECMAScript,ECMAScript核心标准库,扩展自ECMAScript核心标准库的服务端ECMAScript。域...
If your function only takes one parameter, you can omit the parentheses around it. If we take back the above double code:const double = (x) => x * 2; // this arrow function only takes one parameterParentheses around the parameter can be avoided:const double = x => x * 2; // ...
function cube(x) { if (typeof x === 'undefined') { x = 5 } return x * x * x } cube() 1. 2. 3. 4. 5. 6. 7. 8. 9. 相反,使用默认参数可以用更少的代码实现相同的目标。 可以通过使用等式赋值运算符(=)为多维数据集中的参数设置默认值,如下所示: ...
functiondoesXEqualY(x = getRandomNumber(), y = Math.cbrt(cube(x))){returnx === y }doesXEqualY()// true 默认参数甚至可以是函数定义,如本例所示,它将参数定义为内部函数并返回参数的函数调用: functionouter(parameter = function inner() {return100}){returnparameter() ...
Default parameters can be really useful to ensure you have at least an empty array or object literal available when performing operations. Here’s an example with a default parameter: function addToGuestList(guests, list = []) { console.log([...guests, ...list]); } addToGuestList(['Bo...
functionbigFunction(){// code... myvariable; // => undefined // code... var myVariable = 'Initial value'; // code... myVariable; // => 'Initial value'}bigFunction(); 相反,在声明行之前不能访问let(包括const)变量。发生这种情况是因为该变量在声明之前处于[暂时死区](https://rainsoft.io...