Question

Write the syntax of a built in function in JavaScript.

Answer 1

Built in functions(methods) 

1. alert(): 

This is used to display a message(dialogue box) on the screen. 

eg: alert(“Welcome to JS”); 

2. isNaN(): 

To check whether the given value is a number or not. It returns a Boolean value. If the value is not a number(NaN) then this function returns a true value otherwise it returns a false value. 

Eg:

• isNaN(“BVM”); returns true 
• isNaN(8172); returns false 
• isNaN(“680121”); returns false 
• alert(isNaN(8172); displays a message box as false. 

3. toUpperCase(): This is used to convert the text to uppercase. 

Eg: var x=“bvm”; 

alert(x.toUpperCase());

Output is as follows

4. to Lower Case(): This is used to convert the text to lower case. 

Eg: var x=“BVM”; 

alert(x.toLowerCase());

Output is as follows

5. charAt(): It returns the character at a particular position. 

Syntax: variable.charAt(index); 

The index of first character is 0 and the second is 1 and so on.

Eg: 

var x=”HIGHER SECONDARY”; alert(x.charAt(4));

Output is as follows

Eg 2. 

var x=”HIGHER SECONDARY”; 

alert(“The characters @ first position is “+ x.charAt(0));

6. length property: It returns the number of characters in a string.

Syntax: variable.length; 

Eg. 

var x=”HIGHER SECONDARY”; 

alert(“The number of characters is “+ x.length); 

Output is as follows(note that space is a character)