How does += (plus equal) work?

user_747871 0
Viewed 151557

I'm a bit confused with the += sign. How does it work?

  1. 1 += 2 // equals ?

  2. and this

    var data = [1,2,3,4,5];
var sum = 0;
data.forEach(function(value) {
    sum += value; 
});
sum = ?
javascript
14 Answers

that's just a shorthand notation in most languages.which means that

x=x+1;

we can do the same operation for x-=1,x*=1,x/=1; which means

> x=x-1; x=x*1; x=x/1;

user_40039070

x += 1 is just shorthand for x = x + 1 It can also be used for strings:

var string = "foo"
string += "bar"
user_140860210
  1. 1 += 2 won't throw an error but you still shouldn't do it. In this statement you are basically saying "set 1 equal to 1 + 2" but 1 is a constant number and not a variable of type :number or :string so it probably wouldn't do anything. Saying 
    var myVariable = 1
myVariable += 2
console.log(myVariable)
    would log 3 to the console, as x += y is just short for x = x + y
  2. var data = [1,2,3,4,5]
var sum
data.forEach(function(value){
  sum += value
})
    would make sum = 15 because: 
    sum += 1 //sum = 1
sum += 2 //sum = 3
sum += 3 //sum = 6
sum += 4 //sum = 10
sum += 5 //sum = 15
user_124534940
Related