ES6 - Logical operators

Quiz

Assume the value of variable A is 10 and B is 20.

Example

var avg = 20;
var percentage = 90;
console.log("Value of avg: " + avg + " ,value of percentage: " + percentage);
var res = ((avg > 50) && (percentage > 80));
console.log("(avg>50)&&(percentage>80): ", res);
var res = ((avg > 50) || (percentage > 80));
console.log("(avg>50)||(percentage>80): ", res);
var res = !((avg > 50) && (percentage > 80));
console.log("!((avg > 50)&&(percentage>80)): ", res);

The following output is displayed on successful execution of the above code.

Value of avg: 20 ,value of percentage: 90
(avg > 50)&&(percentage > 80): false
(avg > 50)||(percentage > 80): true
!((avg > 50)&&(percentage > 80)): true

Short-circuit Operators

The && and || operators are used to combine expressions.

The && operator returns true only when both the conditions return true. Let us consider an expression −

var a = 10
var result = ( a<10 && a>5)

In the above example, a<10 and a>5 are two expressions combined by an && operator. Here, the first expression returns false. However, the && operator requires both the expressions to return true. So, the operator skips the second expression.

The || operator returns true, if one of the expressions return true. For example −

var a = 10
var result = ( a>5 || a<10)

In the above snippet, two expressions a>5 and a<10 are combined by a || operator. Here, the first expression returns true. Since, the first expression returns true, the || operator skips the subsequent expression and returns true.

Due to this behavior of the && and || operator, they are called as short-circuit operators.

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