JavaScript special characters can be added using backslash() character
The backslash () can be used to insert apostrophes, new lines, quotes, and other special characters into a string.

Example:

var txt

//  Single Quote \'
txt="JavaScript string \'special\' characters.";
alert("Single quote inside sentance in JavaScript String: " +txt);

// Double Quote \"
txt="JavaScript string \"special\" characters.";
alert("Double quote inside sentance in JavaScript String: " +txt);

// Backslash \\
txt="JavaScript string \\special\\ characters.";
alert("BackSlash inside sentance in JavaScript String: " +txt);

// New Line \n
txt="JavaScript string \n special characters.";
alert("New line inside sentance in JavaScript String: " +txt);

// carriage return \r
txt="JavaScript string \r special characters.";
alert("carriage return inside sentance in JavaScript String: " +txt);

// tab \t
txt="JavaScript string \t special characters.";
alert("Tab inside sentance in JavaScript String: " +txt);

// backspace \b
txt="JavaScript string \b special characters.";
alert("BackSpace inside sentance in JavaScript String: " +txt);

//form feed /f
txt="JavaScript string \f special characters.";
alert("Form feed inside sentance in JavaScript String: " +txt);

Live Demo for JavaScript Special Characters