let arr = [3, 5, 5];
let map = {};
for (let i of arr) {
if(map[i]){
map[i] = map[i]++ //<== doesn't work correctly with ++
}else{
map[i] = 1
}
}
console.log(map);
//outputs {3: 1, 5: 1}
Code above outputs {3: 1, 5: 1}, which is incorrect. 5 should be 2, not 1
let arr = [3, 5, 5];
let map = {};
for (let i of arr) {
if(map[i]){
map[i] = map[i]+1 // <== here it works correctly with +1
}else{
map[i] = 1
}
}
console.log(map);
//outputs {3: 1, 5: 2}
Code above outputs {3: 1, 5: 2} correct solution, but why the difference between the two solutions? I thought the ++ is equivalent to +1. But map[i]++ and map[i]+1 give different solutions!
This is because map++ only increments after the line runs, if you use ++map it will increment it before, map + 1 will do the same thing.
let a = 1
let b = 1
console.log(a + b++) // 2let a = 1
let b = 1
console.log(a + ++b) // 3Reference: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Increment#description
++ after a variable by definition adds one to the variable and returns the unchanged value
b=3;
c=b++; //c = 3, b = 4
you can put ++ before a variable to return the value
b=3;
c=++b; //c = 4 b = 4
EDIT: following Randy Casburn's request in the comments, here's a snippet:
var b1 = 3;
var c1 = b1++;
document.getElementById('res1').innerHTML = 'b1 = '+b1+' & c1 = '+c1;
var b2 = 3;
var c2 = ++b2;
document.getElementById('res2').innerHTML = 'b2 = '+b2+' & c2 = '+c2;<p id="res1"></p>
<p id="res2"></p>