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
這只是兩種可能的方式來宣告功能,第二種方式,你可以在宣告之前使用功能。
其他回答
一个重要原因是添加一个和只有一个变量作为你的名称空间的“根”。
var MyNamespace = {}
MyNamespace.foo= function() {
}
或
var MyNamespace = {
foo: function() {
},
...
}
有很多技术来搜索名称,它变得更加重要,有许多可用的JavaScript模块。
此分類上一篇: 如何在JavaScript中宣告名稱空間?
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
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:
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]);
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
}
推荐文章
- Babel 6改变了它导出默认值的方式
- 如何配置历史记录?
- ES6模板文字可以在运行时被替换(或重用)吗?
- [Vue警告]:找不到元素
- 可以在setInterval()内部调用clearInterval()吗?
- AngularJS控制器的生命周期是什么?
- 无法读取未定义的属性“msie”- jQuery工具
- 我的蛋蛋怎么不见了?
- JavaScript中的排列?
- JavaScript中有睡眠/暂停/等待功能吗?
- 如何禁用文本选择使用jQuery?
- 如何停止事件冒泡复选框点击
- 如何在PHP中截断字符串最接近于一定数量的字符?
- 向对象数组添加属性
- 如何在Redux应用程序中动态加载代码分割的减速器?
