为什么在Javascript5严格模式下不允许删除？

Question

我对javascript很新,但我很喜欢它的危险快速和松散的表现力.也就是说,我注意到显然在"使用严格"模式下操作时,您无法删除对象.我不是一个删除东西的忠实粉丝(因为从理论上讲,范围应该照顾到这一点),但我想知道删除这个功能背后的动机是什么？

Answer 1

该delete语句仍然允许在严格模式下,但它的某些特定用途是错误的.它仅允许对象属性,而不是简单名称,并且仅允许可以删除的对象属性.

从而

var a = {x: 0};
delete a.x;

很好,但是

delete Object.prototype;

不是,也不是

delete a;

(后者实际上是语法级错误,而尝试删除不可删除属性是运行时错误.)

Answer 2

[删除] 详细解释举例

// The delete statement is still allowed in strict mode, but some particular uses of it are erroneous. It's only allowed for object properties, not simple names, and only for object properties that can be deleted.

// "use strict";

// creates the property adminName on the global scope
adminName = "xyz";

// creates the property empCount on the global scope
// Since we are using var, this is marked as non-configurable. The same is true of let and const.
var empCount = 43;

EmployeeDetails = {
  name: "xyz",
  age: 5,
  designation: "Developer"
};

// adminName is a property of the global scope.
// It can be deleted since it is created without var.
// Therefore, it is configurable.
console.log("delete adminName =", delete adminName); // returns true

// On the contrary, empCount is not configurable,
// since var was used.
console.log("delete empCount =", delete empCount); // returns false

// delete can be used to remove properties from objects
console.log("delete EmployeeDetails.name =", delete EmployeeDetails.name); // returns true

// Even when the property does not exists, it returns "true"
console.log("delete EmployeeDetails.salary =", delete EmployeeDetails.salary); // returns true

// delete does not affect built-in static properties
console.log("delete Math.PI =", delete Math.PI); // returns false

// EmployeeDetails is a property of the global scope.
// Since it defined without "var", it is marked configurable
console.log("delete EmployeeDetails =", delete EmployeeDetails); // returns true

x = 1;
var y = 2;

function f() {
  var z = 44;

  console.log("delete x =", delete x); // returns true
  console.log("delete y =", delete y); // returns false
  // delete doesn't affect local variable names
  console.log("delete z =", delete z); // returns false
}

f.call();