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2023-02-24 06:00:20

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

函数表达与函数表达的区别:

然而,在变量中存储函数(函数表达)并不是创建函数的唯一方式,也可以通过函数声明进行。

函数表达式可以是匿名的,而函数声明必须有一个名称. 两者都有一个名称属性,用于识别函数. 函数表达式的名称属性是它所属的变量的名称,而函数声明的名称只是给出的名称。

下面是一个例子:

答:

2019-06-20 10:06:36

其他回答

一个描述什么时候优先于第一种方法,而不是第二种方法,是当你需要避免超越一个函数的以前定义时。

与

if (condition){
    function myfunction(){
        // Some code
    }
}

,这个定义的微功能将超越任何以前的定义,因为它将在时间段进行。

虽然

if (condition){
    var myfunction = function (){
        // Some code
    }
}

正确的定义功能工作只有在条件满足时。

2013-03-29 13:26:24

我更喜欢将函数定义为变量:

let first = function(x){
   return x[0];
}

而不是:

function first(){
    ....
}

因为我可以在定义函数时使用表达式和装饰器,例如:

let safe = function(f){
  try {f()...}
}
let last = safe(function(x){return x[0]}).

此外,在 ES6 中,它更短:

 let last = x => x[0]
 ...........
 function last(x){
     return x[0];
 }
......

let last = safe(x => x[0]);
2018-03-08 11:49:32

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'));

V8

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

二是定义函数的不同方式,区别在于浏览器如何解释并将其加载到执行背景中。

第一個案例是函數表達,只有當翻譯者達到這個代碼線時才會充電,因此,如果你這樣做,你會發現函數一不是函數的錯誤。

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

原因在于,在第一行中,没有值被分配到函数One,因此它是不定义的,我们试图称之为函数,因此我们得到一个错误。

在第二行中,我们将匿名函数的参考归分为函数One。

第二个案例是功能声明,在任何代码执行之前加载,所以如果你喜欢下一个,你不会得到任何错误,因为声明加载,在代码执行之前。

functionOne();
function functionOne() {
   // Some code
}
2015-12-28 20:18:03 

function xyz(){
  function abc(){};
  // abc is defined here...
}
// ...but not here

其次,可以结合两种风格:

var xyz = function abc(){};


var xyz = function abc(){
  // xyz is visible here
  // abc is visible here
}
// xyz is visible here
// abc is undefined here


function abc(){};
var xyz = abc;


console.log(xyz === abc); // prints "true"


function abc(){};
console.log(abc.name); // prints "abc"


var abc = function(){};
console.log(abc.name); // prints ""

它的名字是空的 - 我们创建了一个匿名函数,并将其分配给一些变量。

使用合并风格的另一个好理由是使用一个简短的内部名称来引用自己,同时为外部用户提供一个长而不冲突的名称:

// Assume really.long.external.scoped is {}
really.long.external.scoped.name = function shortcut(n){
  // Let it call itself recursively:
  shortcut(n - 1);
  // ...
  // Let it pass itself as a callback:
  someFunction(shortcut);
  // ...
}

在上面的例子中,我们可以用外部名称做同样的事情,但它会太不多(而且更慢)。

function abc(){}

abc在这里在当前范围内在任何地方都被定义:

// We can call it here
abc(); // Works

// Yet, it is defined down there.
function abc(){}

// We can call it again
abc(); // Works


// We can call it here
abc(); // Works
return;
function abc(){}

这是一个功能表达:

var xyz = function(){};

xyz 在这里从分配点定义:

// We can't call it here
xyz(); // UNDEFINED!!!

// Now it is defined
xyz = function(){}

// We can call it here
xyz(); // works

函数声明与函数表达是格雷格所证明的差异的真正原因。

有趣的事实:

var xyz = function abc(){};
console.log(xyz.name); // Prints "abc"


var abc = function(){};

我知道我定义了函数本地,当我定义了函数如

abc = function(){};


function abc(){};

它取决于背景,可能会让你猜测它实际上在哪里定义,特别是在 eval()的情况下 - 答案是: 它取决于浏览器。

2008-12-03 17:43:35

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