CODEWITHSUNDEEP
javascriptoperators
Alexander
Alexander

Reputation: 93

The assignment operator in JavaScript

I have this simple code on the JavaScript.

var a = 10;
var b = 20;

a=a+b-(b=a);

document.write("a = " + a + "</br> b = " + b);

Can somebody explain me, how did these variables change the values and how is the assignment operator works in this case ? I think, that on the first step the variable b is rewrote by number from a: (b=a).

Upvotes: 0

Views: 339

Answers (3)

Bergi
Bergi

Reputation: 664548

It's evaluated outside-in, from left to right, as usually.
The assignment expression returns the assigned value.

a = a + b - (b = a);    // a=10 b=20
a = 10 + b -( b = a);   // a=10 b=20
a = 10 + 20 - (b = a);  // a=10 b=20
a = 30 - (b = a);       // a=10 b=20
a = 30 - (b = 10);      // a=10 b=20
a = 30 - (10);          // a=10 b=10
a = 30 - 10;            // a=10 b=10
a = 20;                 // a=10 b=10
20;                     // a=20 b=10

Upvotes: 2

Christopher Messer
Christopher Messer

Reputation: 2090

Simple explanations below.

1 . We are assigning our initial values:

var a = 10;
var b = 20;

2 . Here we're saying a is equal to 10+20 - (10). Therefore a is now equal to 20 and b is equal to 10 as it was assigned to be a before we assigned a's new value.

a=a+b-(b=a);

3 . Result:

var a = 10;
var b = 20;

a = a + b - (b = a);

console.log("a = " + a); // a = 20
console.log("b = " + b); // b = 10

Upvotes: 1

SkiZer0
SkiZer0

Reputation: 21

Well, let's look closely at this: a = a + b - (b = a);

Let's replace variables with values a = (10 + 20) - (10)

This is because B == 20 until redefined at the end of the expression.

Upvotes: 0

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