这 delete

var

var g_a = 1; //create with var, g_a is a variable
delete g_a; //return false
console.log(g_a); //g_a is still 1

g_b = 1; //create without var, g_b is a property
delete g_b; //return true
console.log(g_b); //error, g_b is not defined

变量

g_a VariableEnvironment “附加到当前作用域-在使用的情况下,这可能是函数执行上下文 变量 在函数内部(尽管当你考虑 let 多变的环境 window ).

参考文献 多变的环境 ECMAScript 10.5 eval 变量 无法删除。

变量

当尝试在不使用的情况下为名称赋值时 变量 LexicalEnvironment 词汇环境 词汇环境 词汇环境 ,它看起来像父母 词汇环境 (详见 10.3.1 和 10.2.2.1 ).顶层 词汇环境 global environment 变量 在当前作用域或任何外部作用域中的关键字,JavaScript最终将获取 窗口 反对作为参考。正如我们之前所了解的,可以删除对象的属性。

备注

1. 重要的是要记住 变量 变量 a 多变的环境 而不是 窗口 财产及其价值将是 10 在代码末尾:

   function test() { a = 5; var a = 10; }
   

2. 上述讨论是在未启用“严格模式”时进行的。当使用“严格模式”时,查找规则有点不同,在没有“严格模式“的情况下,解析为窗口属性的词法引用将在“严格模式下”引发“未声明的变量”错误。我真的不明白这是在哪里指定的,但它是浏览器的行为方式。

scunliffe's answer

delete window.some_var;

删除 当目标不是对象属性时,应该是no操作。例如。,

(function() {
   var foo = 123;
   delete foo; // wont do anything, foo is still 123
   var bar = { foo: 123 };
   delete bar.foo; // foo is gone
}());

但由于全局变量实际上是窗口对象的成员,因此它是有效的。

删除 变得更加复杂,因为它只从目标对象中删除属性,而不是原型。例如。,

function Foo() {}
Foo.prototype = { bar: 123 };
var foo = new Foo();
// foo.bar is 123
foo.bar = 456;
// foo.bar is now 456
delete foo.bar;
// foo.bar is 123 again.

所以要小心。

注:我的答案是 somewhat inaccurate (见最后的“误解”)。该链接解释了所有血腥的细节,但总结是,浏览器之间可能存在很大差异,具体取决于您要删除的对象。 delete object.someProp object !== window 。我仍然不会用它来删除用声明的变量 var

如果你隐式声明变量而没有 var ,正确的方法是使用 delete foo .

ReferenceError 将被抛出,因为您无法将字符串添加到未声明、未定义的标识符中。例子:

x = 5;
delete x
alert('foo' + x )
// ReferenceError: x is not defined

foo = false

null , false , undefined , 0 , NaN ,或 '' !== 操作员,而是 != == false 和 false == undefined ).

还需注意的是 delete 不“删除”引用,而只是直接在对象上删除属性,例如:

bah = {}, foo = {}; bah.ref = foo;

delete bah.ref;
alert( [bah.ref, foo ] )
// ,[object Object] (it deleted the property but not the reference to the other object)

如果你声明了一个变量 变量 您无法删除它:

(function() {
    var x = 5;
    alert(delete x)
    // false
})();

js> var x
js> delete x
false

Math.PI :

js> delete Math.PI
false

删除 与任何语言一样,如果你足够关心,你应该阅读:

• https://developer.mozilla.org/en/Core_JavaScript_1.5_Reference/Operators/Special_Operators/delete_Operator
• http://www.ecma-international.org/publications/files/ECMA-ST/ECMA-262.pdf

看 noah's answer 有关完整详细信息

//Option A.) set to null
some_var = null;

//Option B.) set to undefined
some_var = undefined;

//Option C.) remove/delete the variable reference
delete obj.some_var
//if your variable was defined as a global, you'll need to
//qualify the reference with 'window'
delete window.some_var;

参考文献

• MDN delete API

• MDN SyntaxError when deleting an unqualified variable name in strict mode

TLDR:简单定义的变量(没有 var , let , const )可以删除 delete 。如果您使用 变量 , 让 , 常量 -它们也无法删除 删除 也不与 Reflect.deleteProperty .

铬55:

simpleVar = "1";
"1"
delete simpleVar;
true
simpleVar;
VM439:1 Uncaught ReferenceError: simpleVar is not defined
    at <anonymous>:1:1
(anonymous) @ VM439:1
var varVar = "1";
undefined
delete varVar;
false
varVar;
"1"
let letVar = "1";
undefined
delete letVar;
true
letVar;
"1"
const constVar="1";
undefined
delete constVar;
true
constVar;
"1"
Reflect.deleteProperty (window, "constVar");
true
constVar;
"1"
Reflect.deleteProperty (window, "varVar");
false
varVar;
"1"
Reflect.deleteProperty (window, "letVar");
true
letVar;
"1"

Firefox Nightly 53.0a1显示了相同的行为。

公认的答案(和其他答案)已经过时了!

太长,读不下去了

• delete 删除变量 .
  

• 就是简单地将变量设置为 null . _{source )}
  内存中的变量。)

例子:

x = null;

使用 删除 mark-and-sweep garbage-collection unreachable “(决定代码是否仍然需要它们)。

使用JavaScript,在所有现代浏览器中:

• 对象在内存中保留时 reachable .
• 可到达的 :一组相互链接的对象可能无法作为一个整体访问。 _{( source )}

这 删除 操作员仅用于 删除属性 删除变量。

与普遍看法不同(可能是由于其他编程语言,如 delete in C++ 删除 _{( source )}

strict mode ( 'use strict'; ,而不是常规/ "sloppy mode" )尝试删除变量将引发错误,这是不允许的。JavaScript中的普通变量不能使用 删除 操作员 _{( 来源 )}

…唉,唯一的解决方案是:

Freeing the contents of a variable

null :

var x;

// ...

x = null;    // (x can now be garbage collected)

^{( 来源 )}

• Memory Management (MDN文档)
• Garbage Collection (雷布罗大学)
• The Very Basics of Garbage Collection (javascript.info)
• Understanding JavaScript Memory Management using Garbage Collection
• Eradicating Memory Leaks In Javascript

Reflect.deleteProperty() :

Reflect.deleteProperty(myObject, 'myProp');
// it is equivalent to:
delete myObject.myProp;
delete myObject['myProp'];

window

Reflect.deleteProperty(window, 'some_var');

false (以及 delete operator ).在其他情况下,它会返回 true :

Object.defineProperty(window, 'some_var', {
    configurable: false,
    writable: true,
    enumerable: true,
    value: 'some_val'
});

var frozen = Object.freeze({ myProperty: 'myValue' });
var regular = { myProperty: 'myValue' };
var blank = {};

console.log(Reflect.deleteProperty(window, 'some_var')); // false
console.log(window.some_var); // some_var

console.log(Reflect.deleteProperty(frozen, 'myProperty')); // false
console.log(frozen.myProperty); // myValue

console.log(Reflect.deleteProperty(regular, 'myProperty')); // true
console.log(regular.myProperty); // undefined

console.log(Reflect.deleteProperty(blank, 'notExistingProperty')); // true
console.log(blank.notExistingProperty); // undefined

deleteProperty delete

'use strict'

var frozen = Object.freeze({ myProperty: 'myValue' });

Reflect.deleteProperty(frozen, 'myProperty'); // false
delete frozen.myProperty;
// TypeError: property "myProperty" is non-configurable and can't be deleted

delete 回报 true

implicit_global = 1;
delete implicit_global; // true

window.explicit_global = 1;
delete explicit_global; // true

const _object = {property: 1};
delete _object.property; // true

function_set = function() {};
delete function_set; // true

function function_declaration() {};
delete function_declaration; // false

(function () {
    var _var = 1;
    console.log(delete _var); // false
    console.log(_var); // 1
})()

(function () {
    let _let = 1;
    console.log(delete _let); // false
    console.log(_let); // 1
})()

(function () {
    const _const = 1;
    console.log(delete _const); // false
    console.log(_const); // 1
})()

与简单属性相比,变量具有以下属性 删除

但是,在一个执行上下文中,此规则不受影响。这是 评估 上下文:没有为变量设置[[可配置]]属性。

delete运算符从对象中删除属性。

delete object.property
delete object['property']

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/delete

delete some_var;
delete window.some_var;
delete window['some_var'];

var x; x delete delete x;

只需将变量清零,然后显式检查它是否为null。为什么要费心从作用域中删除变量?这有什么目的是无效不能实现的?

foo = null;
if(foo === null) or if(foo !== null)