4 sentences to understand the addition and subtraction in js

in conclusion:

1. Pre-addition: ++ a == a + = 1 == a = a + 1
2. Add after adding: a++, keep itself unchanged, let the following element with the same name perform +1 operation.
3. For a, whether it is pre-addition or post-addition, it is the number of operators plus the initial value. There are x operators that are x+initial value
4. The principle of subtraction is the same as addition

example

1. Plus plus

var a = 1;
b = ++a + ++a +3 + ++a;
console.log(a);//a等于4
console.log(b);//b等于12

Analysis of calculation process
2. Post-addition

var a = 1;
var b = a++ + a++ +3 + a++;
console.log(b)；//b等于9

Operational process analysis
3. Pre-addition and post-addition mixing

var a = 1;
var b = a++ + ++a + ++a -2 + a++ +1 + a++ + ++a ;
console.log(b);//b等于23

The principle of subtraction and subtraction is the same as that of addition and addition in the calculation process .

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