Javascript-如何在不重新分配对象属性的情况下更改它们 [英] Javascript - How change object properties without reassign them

问题描述

下面的代码片段暴露了疑问

The snippet below exposes the doubt

var foo = 'something'
var baz = 'other thing'

var obj = {
  prop1 : 'my prop',
  prop2 : foo,        //referencing external variable
  prop3 : baz         //referencing external variable
}

// here we get the expected obj to be printed
console.log(obj)

// now I change one of the initial variable
foo = 'changed'

// here we get the sabe print as the first, that is the ~problem~   
console.log(obj)

因此，如何在不重新分配 obj.prop2 = foo

So, how to print 'changed' on prop2 without reassign obj.prop2 = foo

推荐答案

执行时

var obj = {
  prop1 : 'my prop',
  prop2 : foo,        //referencing external variable
  prop3 : baz         //referencing external variable
}

prop2 与变量 foo (或 prop3 和 baz).发生的一切是读取 foo 的当前值，并将其存储在 prop2 中(对于 baz 和 prop3 ).

there is no ongoing link between prop2 and the variable foo (or prop3 and baz). All that happens is that the current value of foo is read, and stored in prop2 (and the same for baz and prop3).

如果您需要 prop2 和 prop3 保持链接到 foo 和 baz ，则可以将它们设置为属性与 getters .这些属性是在读取时触发函数调用的属性(还有设置属性时触发函数调用的 setters ):

If you need prop2 and prop3 to remain linked to foo and baz, you could make them properties with getters. These are properties that trigger a function call when they're read (there are also setters which trigger a function call when the property is set):

var obj = {
  prop1 : 'my prop',
  get prop2() { return foo; },
  get prop3() { return baz; }
};

访问 obj.prop2 是隐藏的函数调用.由于该函数在 foo 上关闭，因此它将返回 foo 的当前值.

Accessing obj.prop2 is a hidden function call. Since the function closes over foo, it returns foo's current value.

实时示例:

var foo = 'something';
var baz = 'other thing';

var obj = {
  prop1 : 'my prop',
  get prop2() { return foo; },
  get prop3() { return baz; }
};

console.log(obj);

foo = 'changed';

console.log(obj);

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