TypeScript - Nested if statement

The else…if ladder is useful to test multiple conditions. Its syntax is given below −


if (boolean_expression1) { 
   //statements if the expression1 evaluates to true 
} else if (boolean_expression2) { 
   //statements if the expression2 evaluates to true 
} else { 
   //statements if both expression1 and expression2 result to false 

When using if…else…if and else statements, there are a few points to keep in mind.

  • An if can have zero or one else's and it must come after any else..if's.

  • An if can have zero to many else..if's and they must come before the else.

  • Once an else..if succeeds, none of the remaining else..if's or else's will be tested.

Example: else…if ladder

var num:number = 2 
if(num > 0) { 
   console.log(num+" is positive") 
} else if(num < 0) { 
   console.log(num+" is negative") 
} else { 
   console.log(num+" is neither positive nor negative") 

The snippet displays whether the value is positive, negative or zero.

On compiling, it will generate the following JavaScript code −

//Generated by typescript 1.8.10
var num = 2;
if (num > 0) {
   console.log(num + " is positive");
} else if (num < 0) {
   console.log(num + " is negative");
} else {
   console.log(num + " is neither positive nor negative");

Here is the output of the above code −

2 is positive