为什么以下JavaScript代码无效？

Question

When the following code is executed in chrome console

let a, b, c;
b = 2;
a = b+1 = c = 2+3;

It says an error 'Invalid left-hand side assignment' for the last statement. But when we execute the below-given code it accepts it and does not show any error.

let a, b, c;
a = b = c = 2+3;

assignment '=' is an operator so according to operator precedence in javascript, it should work fine. what do you guys think, what is the problem?

Answer 1

for the first code you would need to do

let a,b,c;
b=2;
a=b+1;
c=5;

doing

a=b=c=2+3

works because you arent altering a value to the left of the last equal

Answer 2

the = operator calculate first the right side and require the left side to be lvalue .

In your second example for every assignment operator the left side is always a variable, so it works fine. but in the first example:

let a, b, c;

b = 2;

a = b+1 = c = 2+3;

you trying to assign 5 into b+1 , its simply not a variable.

Answer 3

您只需要一些括号即可清楚说明您的意思：

 a = 1 + (b = c = 2+3);