More on Operators

The JavaScript execution sequence is one statement at-a-time, left-to-right (like we would read English). However operators and certain programming constructs(if/else, for, while etc.) can alter this. We now look at how operators affect the execution sequence.

Operator Precedence

Consider the assignment operator:

var x = 2 + 3;

The assignment operator has 2 operands, commonly known as the left-hand-side (var x) and the right-hand-side (2 + 3). The default execution sequence dicatates that the left-hand-side be evaluated by the interpreter first. The assignment operator changes this. It dictates that the right-hand-side is evaluated first. Thus the expression 2 + 3 is evaluated (5) and then is assigned to the left-hand-side. That is, the variable declaration and assignment happens after the right-hand-side expression is evaluated.

All other operators also alter the execution sequence. The interpreter uses the precedence order to evaluate operators. The following table lists the precedence of each JS operator.

Operator Polymorphism

The same operator can perform different operations depending on the operands provided to it. This is known as operator polymorphism.

This concept is best explained using the addition(+) operator.

Look at the following examples:

var num = 10;
var st = "hello";

typeof num; // "number"
typeof st; // "string"

var x = num + 20; // 30
typeof x; // "number"

var y = st + "world"; // "hello world"
typeof y; // "string"

var z = num + st; "10hello"
typeof z; // "string"

z = st + num; "hello10"
typeof z; // "string"

Comparison Operators

These are binary operators that compare if the operands are equal to, greater than, less than etc.

Logical Operators

These operators can be used to combine 2 comparison operators. The operands are Boolean (or else they are typecast to Boolean).