赋值后变量值未更新

Question

var a = 2;
var b = a;

console.log( b ); //2

a= 5;

console.log( b ); //2

Q: Why variable 'b' is getting value 2 even when variable 'a' is assigned a different value

Answer 1

console.log(b)返回2因为当您访问基本类型时，您将直接使用其值。

Answer 2

Cause numbers are immutable.

Changing an immutable value, replaces the original value with a new value, hence the original value is not changed (thats why b = 2 ).

If you need a reference, use object and/or arrays var a ={value: 2}, b = a a.value = 3 // also changes the value of be, since it can mutate

Answer 3

在javascript中，图元（数字，布尔值，字符串）由值分配，只有对象由引用分配。

Answer 4

In Javascript, integers are immutable . It means that the object's value once assigned cannot change. When you do

a=5;
b=a;

It is true that both are names of the same object whose value is 5 . Later when you do -

a=2

It assigns the reference a a new object whose value is 2. So essentially a now points to a new object. Ans both objects exist.

For a better understanding you can refer to this link

Answer 5

When doing Assignment of primitive values in javascript:

It's important to point out that this assignment does not tie a and b together. In fact all that happened was that the value from a was copied into b , so when we go to change a we don't have to worry about affecting b . This is because the two variables are backed by two distinct memory locations – with no crossover.

In brief way:

When you assign b = a

Actually you didn't copy the reference of a variable and make b point to the same variable location in memory.

You only copy the value of a variable and put it in new variable b with different memory location.