var functionName = 函数() {} vs 函数函数Name() {}

我最近开始保持别人的JavaScript代码,我正在修复错误,添加功能,也试图更新代码并使其更加一致。

以前的开发人员使用了两种方式来宣布功能,我无法解决是否有原因。

兩種方式是:

var functionOne = function() {
    // Some code
};

function functionTwo() {
    // Some code
}

使用这两种不同的方法的原因是什么?每个方法的优点和缺点是什么?可以用一种方法做些什么,不能用另一种方法做些什么?

当前回答

1、功能表达

var functionOne = function() {
    // Some code
};

函数表达式定义一个函数作为一个更大的表达式合成的一部分(通常是一个变量任务)。函数表达式通过函数表达式定义的函数可以被命名或匿名。

二、职能宣言

function functionTwo() {
    // Some code
}

这是在JavaScript中召唤函数的正常方式,这个函数可以被召唤之前你甚至宣布它,因为在JavaScript中,所有函数都被收集,但如果你有“严格使用”这个函数不会像预期那样收集,这是一个很好的方式召唤所有正常函数,这些函数不大,也不是一个构建函数。

此外,如果您需要更多关于如何在JavaScript中工作的信息,请参阅下面的链接:

2017-05-09 13:56:36

其他回答

我正在列出下面的差异:

函数声明可以在代码中的任何地方放置。即使它在定义在代码中出现之前被引用,它也被执行,因为函数声明被承诺记忆或以某种方式被加密,在页面上的任何其他代码开始执行之前。查看下面的函数: 函数外部函数() {函数 foo() { 返回 1; } 返回 foo(); 函数

2015-09-09 10:30:53

函数One = 函数() {} 定义在运行时间,函数Two() {} 定义在部分时间。

// Run-Time function declaration 
functionOne(); // Calling functionOne function here will give an Error
var functionOne = function () {
  // Some code
};

// Parse-Time function declaration 
functionTwo(); // Calling functionTwo function will not give an Error
function functionTwo() {
  // Some code...
}

此分類上一篇: Run-time vs Parse-time javascript run-time vs parse-time

2020-03-03 08:43:56

谈到全球背景,这两种说法和函数声明最终将为全球对象创造一个不可分割的财产,但两者的价值可以被夸张。

两种方式之间的微妙区别在于,当变量定位过程运行(在实际代码执行之前)时,与 var 所宣布的所有标识符将以未定义的标识符开始,并且由 FunctionDeclaration 所使用的标识符将从那时起可用,例如:

 alert(typeof foo); // 'function', it's already available
 alert(typeof bar); // 'undefined'
 function foo () {}
 var bar = function () {};
 alert(typeof bar); // 'function'

 function test () {}
 test = null;

你的两个例子之间的另一个显而易见的区别是,第一个函数没有名字,而第二个函数有它,这在解体时可能非常有用(即检查一个呼叫板)。

此外,未透露的任务在严格模式下在 ECMAScript 5 上投下参考错误。

必须读一读:

名称函数表达解密

2010-08-08 19:32:11

你在那里发布的两个代码剪辑,几乎所有目的都会以相同的方式行事。

然而,行为的差异是,在第一个变量(有函数One = 函数() {}),该函数只能在代码中的那个点之后被称为。

第二个选项(函数Two()),函数可用于代码,运行在函数被宣布的地方。

这是因为第一种变量,函数在运行时分配给变量foo;第二种函数在运行时分配给这个识别器,foo。

更多技术信息

JavaScript 有三种方式来定义功能。

你的第一个剪辑显示一个函数表达式. 这意味着使用“函数”操作员创建一个函数 - 该操作员的结果可以存储在任何变量或对象属性. 函数表达式是强大的这种方式. 函数表达式经常被称为“匿名函数”,因为它不需要一个名字, 你的第二个例子是一个函数声明。

2010-04-20 04:54:49

鉴于“名称函数在轨道上出现”的论点,现代的JavaScript引擎实际上非常能够代表匿名函数。

至于这篇文章,V8,SpiderMonkey,Chakra和Nitro总是提到他们的名字命名的函数,他们几乎总是提到一个匿名函数,它的识别器,如果它有一个。

SpiderMonkey 可以从另一个函数返回的匿名函数的名称。

如果你真的,真的想要你的 iterator 和成功的呼叫回复出现在轨道上,你可以命名那些也。

[].forEach(function iterator() {});

但是,大多数情况下,它不值得强调。

哈里斯(Fiddle)

'use strict';

var a = function () {
    throw new Error();
},
    b = function b() {
        throw new Error();
    },
    c = function d() {
        throw new Error();
    },
    e = {
        f: a,
        g: b,
        h: c,
        i: function () {
            throw new Error();
        },
        j: function j() {
            throw new Error();
        },
        k: function l() {
            throw new Error();
        }
    },
    m = (function () {
        return function () {
            throw new Error();
        };
    }()),
    n = (function () {
        return function n() {
            throw new Error();
        };
    }()),
    o = (function () {
        return function p() {
            throw new Error();
        };
    }());

console.log([a, b, c].concat(Object.keys(e).reduce(function (values, key) {
    return values.concat(e[key]);
}, [])).concat([m, n, o]).reduce(function (logs, func) {

    try {
        func();
    } catch (error) {
        return logs.concat('func.name: ' + func.name + '\n' +
                           'Trace:\n' +
                           error.stack);
        // Need to manually log the error object in Nitro.
    }

}, []).join('\n\n'));

func.name: 
Trace:
Error
    at a (http://localhost:8000/test.js:4:11)
    at http://localhost:8000/test.js:47:9
    at Array.reduce (native)
    at http://localhost:8000/test.js:44:27

func.name: b
Trace:
Error
    at b (http://localhost:8000/test.js:7:15)
    at http://localhost:8000/test.js:47:9
    at Array.reduce (native)
    at http://localhost:8000/test.js:44:27

func.name: d
Trace:
Error
    at d (http://localhost:8000/test.js:10:15)
    at http://localhost:8000/test.js:47:9
    at Array.reduce (native)
    at http://localhost:8000/test.js:44:27

func.name: 
Trace:
Error
    at a (http://localhost:8000/test.js:4:11)
    at http://localhost:8000/test.js:47:9
    at Array.reduce (native)
    at http://localhost:8000/test.js:44:27

func.name: b
Trace:
Error
    at b (http://localhost:8000/test.js:7:15)
    at http://localhost:8000/test.js:47:9
    at Array.reduce (native)
    at http://localhost:8000/test.js:44:27

func.name: d
Trace:
Error
    at d (http://localhost:8000/test.js:10:15)
    at http://localhost:8000/test.js:47:9
    at Array.reduce (native)
    at http://localhost:8000/test.js:44:27

func.name: 
Trace:
Error
    at e.i (http://localhost:8000/test.js:17:19)
    at http://localhost:8000/test.js:47:9
    at Array.reduce (native)
    at http://localhost:8000/test.js:44:27

func.name: j
Trace:
Error
    at j (http://localhost:8000/test.js:20:19)
    at http://localhost:8000/test.js:47:9
    at Array.reduce (native)
    at http://localhost:8000/test.js:44:27

func.name: l
Trace:
Error
    at l (http://localhost:8000/test.js:23:19)
    at http://localhost:8000/test.js:47:9
    at Array.reduce (native)
    at http://localhost:8000/test.js:44:27

func.name: 
Trace:
Error
    at http://localhost:8000/test.js:28:19
    at http://localhost:8000/test.js:47:9
    at Array.reduce (native)
    at http://localhost:8000/test.js:44:27

func.name: n
Trace:
Error
    at n (http://localhost:8000/test.js:33:19)
    at http://localhost:8000/test.js:47:9
    at Array.reduce (native)
    at http://localhost:8000/test.js:44:27

func.name: p
Trace:
Error
    at p (http://localhost:8000/test.js:38:19)
    at http://localhost:8000/test.js:47:9
    at Array.reduce (native)
    at http://localhost:8000/test.js:44:27 test.js:42

蜘蛛侠

func.name: 
Trace:
a@http://localhost:8000/test.js:4:5
@http://localhost:8000/test.js:47:9
@http://localhost:8000/test.js:54:1


func.name: b
Trace:
b@http://localhost:8000/test.js:7:9
@http://localhost:8000/test.js:47:9
@http://localhost:8000/test.js:54:1


func.name: d
Trace:
d@http://localhost:8000/test.js:10:9
@http://localhost:8000/test.js:47:9
@http://localhost:8000/test.js:54:1


func.name: 
Trace:
a@http://localhost:8000/test.js:4:5
@http://localhost:8000/test.js:47:9
@http://localhost:8000/test.js:54:1


func.name: b
Trace:
b@http://localhost:8000/test.js:7:9
@http://localhost:8000/test.js:47:9
@http://localhost:8000/test.js:54:1


func.name: d
Trace:
d@http://localhost:8000/test.js:10:9
@http://localhost:8000/test.js:47:9
@http://localhost:8000/test.js:54:1


func.name: 
Trace:
e.i@http://localhost:8000/test.js:17:13
@http://localhost:8000/test.js:47:9
@http://localhost:8000/test.js:54:1


func.name: j
Trace:
j@http://localhost:8000/test.js:20:13
@http://localhost:8000/test.js:47:9
@http://localhost:8000/test.js:54:1


func.name: l
Trace:
l@http://localhost:8000/test.js:23:13
@http://localhost:8000/test.js:47:9
@http://localhost:8000/test.js:54:1


func.name: 
Trace:
m</<@http://localhost:8000/test.js:28:13
@http://localhost:8000/test.js:47:9
@http://localhost:8000/test.js:54:1


func.name: n
Trace:
n@http://localhost:8000/test.js:33:13
@http://localhost:8000/test.js:47:9
@http://localhost:8000/test.js:54:1


func.name: p
Trace:
p@http://localhost:8000/test.js:38:13
@http://localhost:8000/test.js:47:9
@http://localhost:8000/test.js:54:1

查克拉

func.name: undefined
Trace:
Error
   at a (http://localhost:8000/test.js:4:5)
   at Anonymous function (http://localhost:8000/test.js:47:9)
   at Global code (http://localhost:8000/test.js:42:1)


func.name: undefined
Trace:
Error
   at b (http://localhost:8000/test.js:7:9)
   at Anonymous function (http://localhost:8000/test.js:47:9)
   at Global code (http://localhost:8000/test.js:42:1)


func.name: undefined
Trace:
Error
   at d (http://localhost:8000/test.js:10:9)
   at Anonymous function (http://localhost:8000/test.js:47:9)
   at Global code (http://localhost:8000/test.js:42:1)


func.name: undefined
Trace:
Error
   at a (http://localhost:8000/test.js:4:5)
   at Anonymous function (http://localhost:8000/test.js:47:9)
   at Global code (http://localhost:8000/test.js:42:1)


func.name: undefined
Trace:
Error
   at b (http://localhost:8000/test.js:7:9)
   at Anonymous function (http://localhost:8000/test.js:47:9)
   at Global code (http://localhost:8000/test.js:42:1)


func.name: undefined
Trace:
Error
   at d (http://localhost:8000/test.js:10:9)
   at Anonymous function (http://localhost:8000/test.js:47:9)
   at Global code (http://localhost:8000/test.js:42:1)


func.name: undefined
Trace:
Error
   at e.i (http://localhost:8000/test.js:17:13)
   at Anonymous function (http://localhost:8000/test.js:47:9)
   at Global code (http://localhost:8000/test.js:42:1)


func.name: undefined
Trace:
Error
   at j (http://localhost:8000/test.js:20:13)
   at Anonymous function (http://localhost:8000/test.js:47:9)
   at Global code (http://localhost:8000/test.js:42:1)


func.name: undefined
Trace:
Error
   at l (http://localhost:8000/test.js:23:13)
   at Anonymous function (http://localhost:8000/test.js:47:9)
   at Global code (http://localhost:8000/test.js:42:1)


func.name: undefined
Trace:
Error
   at Anonymous function (http://localhost:8000/test.js:28:13)
   at Anonymous function (http://localhost:8000/test.js:47:9)
   at Global code (http://localhost:8000/test.js:42:1)


func.name: undefined
Trace:
Error
   at n (http://localhost:8000/test.js:33:13)
   at Anonymous function (http://localhost:8000/test.js:47:9)
   at Global code (http://localhost:8000/test.js:42:1)


func.name: undefined
Trace:
Error
   at p (http://localhost:8000/test.js:38:13)
   at Anonymous function (http://localhost:8000/test.js:47:9)
   at Global code (http://localhost:8000/test.js:42:1)

尼特

func.name: 
Trace:
a@http://localhost:8000/test.js:4:22
http://localhost:8000/test.js:47:13
reduce@[native code]
global code@http://localhost:8000/test.js:44:33

func.name: b
Trace:
b@http://localhost:8000/test.js:7:26
http://localhost:8000/test.js:47:13
reduce@[native code]
global code@http://localhost:8000/test.js:44:33

func.name: d
Trace:
d@http://localhost:8000/test.js:10:26
http://localhost:8000/test.js:47:13
reduce@[native code]
global code@http://localhost:8000/test.js:44:33

func.name: 
Trace:
a@http://localhost:8000/test.js:4:22
http://localhost:8000/test.js:47:13
reduce@[native code]
global code@http://localhost:8000/test.js:44:33

func.name: b
Trace:
b@http://localhost:8000/test.js:7:26
http://localhost:8000/test.js:47:13
reduce@[native code]
global code@http://localhost:8000/test.js:44:33

func.name: d
Trace:
d@http://localhost:8000/test.js:10:26
http://localhost:8000/test.js:47:13
reduce@[native code]
global code@http://localhost:8000/test.js:44:33

func.name: 
Trace:
i@http://localhost:8000/test.js:17:30
http://localhost:8000/test.js:47:13
reduce@[native code]
global code@http://localhost:8000/test.js:44:33

func.name: j
Trace:
j@http://localhost:8000/test.js:20:30
http://localhost:8000/test.js:47:13
reduce@[native code]
global code@http://localhost:8000/test.js:44:33

func.name: l
Trace:
l@http://localhost:8000/test.js:23:30
http://localhost:8000/test.js:47:13
reduce@[native code]
global code@http://localhost:8000/test.js:44:33

func.name: 
Trace:
http://localhost:8000/test.js:28:30
http://localhost:8000/test.js:47:13
reduce@[native code]
global code@http://localhost:8000/test.js:44:33

func.name: n
Trace:
n@http://localhost:8000/test.js:33:30
http://localhost:8000/test.js:47:13
reduce@[native code]
global code@http://localhost:8000/test.js:44:33

func.name: p
Trace:
p@http://localhost:8000/test.js:38:30
http://localhost:8000/test.js:47:13
reduce@[native code]
global code@http://localhost:8000/test.js:44:33

2014-10-12 00:58:57

var functionName = 函数() {} vs 函数函数Name() {}

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