How javascript represents a null pointer

In javascript, null is used to represent a null pointer. The main purpose of null is to replace the assignment with a null when the assignment is uncertain, and then reassign the value when it is used later. Use null for the initial assignment, which takes up almost no memory space.

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

Null object pointer null

means none, none, unexpectedly none ==> (I don’t know the value at first, set null manually, and assign it later. Operation, meaning "no object")

let a = null;
// 我们开始不知道给null赋什么值，所以先给它一个空值，等想赋值的时候再给他

let a = 0;
// 有些代码可能会按照这种方式给不确定的值进行赋值，但记住，0是在栈内存中有自己的储存空间的，而null是完完全全的不暂居空间，一般赋空值用null

• The main purpose of null is to replace the assignment with a null when the assignment is uncertain, and then re-assign the value when used later

• Use null for initial assignment, which does not occupy memory space, although only a little bit.

• Any variable pointing to null has no address. null is a null object pointer

Extended information:

undefined undefined

also represents No, none, unexpectedly no ==> (indicates "missing value", that is, there should be a value here, but it has not been defined)

let a;  						// 1. 创建一个变量没有赋值，默认值为undefined
function fn() {}; fn()		 	 // 2. 函数默认 return 返回值为 undefined
function fn(x) {consoloe.log(x)}; fn()	 // 2. 调用函数时没有传递实参给形参，形参为undefined
let obj = {}; obj.name			 // 3. 访问不存在的属性名，返回为undefined
let arr = [, 20, , 'a'];		// 4. 数组中没有给对应的索引号传值，0和1的位置为 undefined

[Recommended learning: javascript advanced tutorial 】

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