What is the plus sign before a function?
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这是bootstrap.js中的js代码
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 | /* ======================================================================== * Bootstrap: collapse.js v3.1.1 * http://getbootstrap.com/javascript/#collapse * ======================================================================== * Copyright 2011-2014 Twitter, Inc. * Licensed under MIT (https://github.com/twbs/bootstrap/blob/master/LICENSE) * ======================================================================== */ +function ($) { 'use strict'; // COLLAPSE PUBLIC CLASS DEFINITION // ================================ ... } |
我见过"；"在函数定义之前避免混合代码。但是"+"符号在函数之前意味着什么？它是否要将返回值转换为字符串？
它通常与IIFE/SIFE一起使用。当您使用这样的
1 2 3 | +function(){ console.log("Welcome"); }() |
产量
1 | Welcome |
当整个函数都用括号括起来时，这是获得相同行为的另一种方法，如下所示
1 2 3 | (function(){ console.log("Welcome"); }()); |
注：不只是
它被称为一元加运算符：
The unary plus operator precedes its operand and evaluates to its
operand but attempts to converts it into a number, if it isn't
already. For example, y = +x takes the value of x and assigns that to
y; that is, if x were 3, y would get the value 3 and x would retain
the value 3; but if x were the string"3", y would also get the value
3