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Operators

Comparison operators

Note the two different uses of the equals sign:
A single equals sign (=) is used to assign a value to a variable.
A triple equals sign (===) is used to compare two values (see Equality Operators).

Equality operators

  • Equality ==
  • Inequality !=
  • Identity / strict equality === (preferred)
  • Non-identity / strict inequality !== (preferred)

How does this work in practice?

1 == 1 // -> true
7 == '7' // -> true
1 != 2  // -> true
5 === 5  // -> true
9 === '9'  // -> false
3 !== 3 // -> false
3 !== '3' // -> true

why does 7 == '7' returns true and 9 === '9' returns false?

We strongly recommend that you always use the strict form when comparing for equality (===) or inequality (!==). Use the non-strict forms only when there is a compelling reason to do so (you will be hard pressed to find such a reason).

Relational operators

  • Greater than operator >
  • Greater than or equal operator >=
  • Less than operator <
  • Less than or equal operator <=
4 > 3   // -> true
3 >= 3  // -> true
13 < 12 // -> false
3 <= 4   // -> true

More about comparison operators

Arithmetic operators

  • Addition +
  • Subtraction -
  • Multiplication *
  • Division /
  • Remainder (sometimes called modulo) %
    Returns the remainder left over after you've shared the left number out into a number of integer portions equal to the right number.
8 + 9 // -> 17, adds two numbers together.
20 - 12 // -> 8, subtracts the right number from the left.
3 * 4 // -> 12, multiplies two numbers together.
10 / 5 // -> 2, divides the left number by the right.
8 % 3 /// -> 2, as three goes into 8 twice, leaving 2 left over.

More about Arithmetic operators

Logical operators

  • AND &&
  • OR ||
true && false //-> false
false && true //-> false
false || true //-> true
true || false //-> true

Given that x = 6 and y = 3

x < 10 && y > 1 // -> true
x === 5 || y === 5 // -> false
x !== y // -> true

Logical NOT

  • NOT !
true === !false
false === !true

More about logical operators

typeof operator

To get the type of a value assigned to a variable, use the following code:

let bar = 42; 
typeof bar    //-> 'number' 
typeof typeof bar; //->  'string'

So the data type of what typeof returns is always a string, bar on the other hand is still a number.

Assignment operators

In addition to the simple assignment operator = there are also compound assignment operators such as +=. The following two assignments are equivalent:

x += 1;
x = x + 1;
Operator Example Same As
= x = y x = y
+= x += y x = x + y
-= x -= y x = x - y
*= x *= y x = x * y
/= x /= y x = x / y
%= x %= y x = x % y

Also check out special characters and their names