JS Logic

The if Statement

Use the if statement to specify a block of JavaScript code to be executed if a condition is true.

Syntax

if (condition) {

block of code to be executed if the condition is true

}

Note that if is in lowercase letters. Uppercase letters (If or IF) will generate a JavaScript error.

Example

Make a «Good day» greeting if the hour is less than 18:00:

if (hour < 18) {

greeting = «Good day»;

}

The result of greeting will be:

Good day

JS Операторы

JavaScript Arithmetic Operators

Arithmetic operators are used to perform arithmetic on numbers:

Operator Description

+ Addition

— Subtraction

* Multiplication

/ Division

% Modulus

++ Increment

— Decrement

JavaScript Assignment Operators

Assignment operators assign values to JavaScript variables.

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

The addition assignment operator (+=) adds a value to a variable.

Example

var x = 10;

x += 5;

JavaScript String Operators

The + operator can also be used to add (concatenate) strings.

Example

txt1 = «John»;

txt2 = «Doe»;

txt3 = txt1 + » » + txt2;

The result of txt3 will be:

John Doe

The += assignment operator can also be used to add (concatenate) strings:

Adding two numbers, will return the sum, but adding a number and a string will return a string:

Example

x = 5 + 5;

y = «5» + 5;

z = «Hello» + 5;

The result of x, y, and z will be:

10

55

Hello5

JavaScript Comparison Operators

Operator Description

== equal to

=== equal value and equal type

!= not equal

!== not equal value or not equal type

> greater than

< less than

>= greater than or equal to

<= less than or equal to

? ternary operator

JavaScript Logical Operators

Operator Description

&& logical and

|| logical or

! logical not

JavaScript Type Operators

Operator Description

typeof Returns the type of a variable

instanceof Returns true if an object is an instance of an object type

Type operators are fully described in the JS Type Conversion chapter.

JavaScript Bitwise Operators

Bit operators work on 32 bits numbers.

Any numeric operand in the operation is converted into a 32 bit number. The result is converted back to a JavaScript number.

Operator Description Example Same as Result Decimal

& AND 5 & 1 0101 & 0001 0001 1

| OR 5 | 1 0101 | 0001 0101 5

~ NOT ~ 5 ~0101 1010 10

^ XOR 5 ^ 1 0101 ^ 0001 0100 4

<< Zero fill left shift 5 << 1 0101 << 1 1010 10

>> Signed right shift 5 >> 1 0101 >> 1 0010 2

>>> Zero fill right shift 5 >>> 1 0101 >>> 1 0010 2

The examples above uses 4 bits unsigned examples. But JavaScript uses 32-bit signed numbers.

Because of this, in JavaScript, ~ 5 will not return 10. It will return -6.

~00000000000000000000000000000101 will return 11111111111111111111111111111010

Bitwise operators are fully described in the JS Bitwise chapter.