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

在计算机科学的意义上,我们谈论匿名函数和名称函数,我认为最重要的区别是匿名函数与名称无关,因此名称匿名函数。

有关匿名功能和Lambda calculus的更多信息,维基百科是一个很好的开始:匿名功能。

2008-12-18 19:30:42

其他回答

a = 10
output : 10

(1 + 3)
output = 4

声明/声明:不返回值的东西示例:

if (1 > 2) {
 // do something. 
}

此分類上一篇

同样,我们有函数声明/声明 vs 函数表达请举一个例子:

// test.js

var a = 10;

// function expression
var fun_expression = function() {
   console.log("Running function Expression");
}

// funciton expression

function fun_declaration() {
   console.log("Running function Statement");
}

重要:在JavaScript引擎运行上面的JS文件时会发生什么。

现在,假设我们更新JS到。

// test.js

console.log(a)  //output: udefined (No error)
console.log(fun_expression)  // output: undefined (No error)
console.log(fun_expression()) // output: Error. As we trying to invoke undefined. 
console.log(fun_declaration()) // output: running function statement  (As fun_declaration is already hoisted in the memory). 

var a = 10;

// function expression
var fun_expression = function() {
   console.log('Running function expression')
}

// function declaration

function fun_declaration() {
   console.log('running function declaration')
}

console.log(a)   // output: 10
console.log(fun_expression()) //output: Running function expression
console.log(fun_declaration()) //output: running function declaration

在评论中提到的结果,应该有助于理解函数表达与函数声明/声明之间的区别。

2018-05-15 00:22:23

var add = undefined; try { console.log(“成功:”,添加(1, 1)); } catch(e) { console.log(“错误:” + e); } add = function(a, b){ return a + b; }

尝试 { console.log(“成功:”,添加(1, 1)); } catch(e) { console.log(“错误:” + e); } var add=function add(a, b){ return a + b; }

名称(名称)

函数函数的名称 thefuncname(){} 是函数名称,当它以这种方式宣布时。

var a = 函数 foobar(){}; console.log(a.name);

变量可变性

什么是“最接近的区块”

正常是 add=function(){}

正常功能添加({})

功能

Arrow 函数与 var add=函数()

Arrow 函数与函数添加()

2018-01-15 01:55:57

我用我的代码中的变量方法出于一个非常具体的原因,其理论已经以抽象的方式被覆盖,但一个例子可以帮助一些像我这样的人,有有限的JavaScript专业知识。

有些品牌需要特定的功能,而有些则不。有时我需要添加新的功能来做新的品牌特定的事情.我很高兴更改共享编码,但我不想需要更改所有160套品牌文件。

使用变量合成,我可以在共享代码中宣言变量(基本上是函数指标),并分配一个三位一体函数,或设置为零。

2012-11-29 11:28:49

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

如果你使用这些功能来创建对象,你会得到:

var objectOne = new functionOne();
console.log(objectOne.__proto__); // prints "Object {}" because constructor is an anonymous function

var objectTwo = new functionTwo();
console.log(objectTwo.__proto__); // prints "functionTwo {}" because constructor is a named function

2013-10-25 16:38:22

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

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