Nested if statements

A nested if statement in TypeScript is an if statement that is present inside the body of another if or else statement. The else…if ladder is a type of nested if statement. The nested if statement or else…if ladder is useful to test multiple conditions. Its syntax is given below −

Syntax

if(boolean_expression1){//statements if the expression1 evaluates to true }elseif(boolean_expression2){//statements if the expression2 evaluates to true }elseif(boolean_expression3){//statements if the expression3 evaluates to false }else{//statements if all three boolean expressions 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: elseif ladder

var num:number=2if(num >0){console.log(num&plus;" is positive")}elseif(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 1.8.10var num =2;if(num >0){console.log(num +" is positive");}elseif(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