JavaScript delete运算符详解：原理、限制与最佳实践

var x = { a: 1 };
delete x.a; // true
x.a; // undefined

var x = 1;
delete x; // false;
x; // 1

function x() {};
delete x; // false;
typeof x; // "function"

var GLOBAL_OBJECT = this;

var foo = 1;
delete foo; // false
typeof foo; // "number"
/* 'bar

function bar() {};
delete bar; // false
typeof bar; // "function"

GLOBAL_OBJECT.baz = "baz";
delete GLOBAL_OBJECT.baz; // true
typeof GLOBAL_OBJECT.baz; // "undefined"

(function() {
  //不能删除'arguments'，因为有DontDelete
  delete arguments; // false;
  typeof arguments; // "object"

  //也不能删除函数的length,因为有DontDelete
  function f() {};
  delete f.length; // false;
  typeof f.length; // "number"
}) ();

(function(foo,bar) {
  delete foo; // false
  foo; // 1

  delete bar; // false
  bar; // "bah"
}) (1,"bah");

var GLOBAL_OBJECT = this;

/* 通过变量声明生成全局对象的属性，拥有DontDelete */
var foo = 1;

/* 通过未声明的变量赋值生成全局对象的属性，没有DontDelete */
bar = 2;
delete foo; // false
delete bar; // true

/* 'foo'创建的同时生成DontDelete */
function foo() {};
/* 之后的赋值过程不改变已有属性的内部属性，DontDelete仍然存在 */
foo = 1;
delete foo; // false;
typeof foo; // "number"
/* 但赋值一个不存在的属性时，创建了一个没有内部属性的属性，因此没有DontDelete */
this.bar = 1;
delete bar; // true;
typeof bar; // "undefined"

var Benjamin = {
  "name": "zuojj",
  "url" : "http://www.zuojj.com"
};
delete Benjamin.name;
//Outputs: Object { url: "http://www.zuojj.com" }
console.log(Benjamin);

var benjamin = "http://www.zuojj.com";
delete benjamin;
//Outputs: "http://www.zuojj.com"
console.log(benjamin);

// Because var isn't used, this is a property of window
benjamin = "zuojj";
delete window.benjamin;
// ReferenceError: benjamin is not defined
console.log(benjamin);

var benjamin = {
  "name": "zuojj",
  "url" : "http://www.zuojj.com"
};
var nameDeleted = delete benjamin.name;
// Outputs: true
console.log(nameDeleted);
"use strict";
var benjamin_ = "zuojj";
//Outputs: Uncaught SyntaxError: Delete of an unqualified identifier in strict mode.
delete benjamin_;

var benjamin = {
  "name": "zuojj",
  "url" : "http://www.zuojj.com"
};
benjamin.name = null;

// Outputs: Object { name: null, url: "http://www.zuojj.com" }
console.log(benjamin);

var name   = "zuojj",
    benjamin = {};
benjamin.name = name;
delete benjamin.name;
//Outputs: "zuojj"
console.log(name);