COM271, Week 10

Number and String Objects

Syllabus | Table of Pages | Assignments | References and Useful Links

Number

See W3Schools Number Object for full list of all properties and methods: www.w3schools.com/jsref/jsref_obj_number.asp

The number ( ) object corresponds to the primitive number data type. Its toString ( ) method converts a number into a character string. The method toFixed restricts a number to a set number of decimal places:
var pi = 3.14159;
var n=pi.toFixed(2);
returns n=3.14.

String

See W3Schools String Object of properties and methods: www.w3schools.com/jsref/jsref_obj_string.asp

See also the W3Schools tutorial for string: http://www.w3schools.com/js/js_obj_string.asp

The String object contains all the methods for string manipulation and examination, substring extraction, and conversion to marked-up HTML . The only String ( ) property is string.length. No method operates on the string in place. You must assign the results of a string method back to the string to effect a change in the string. Examples of string methods:

• toUpperCase ( ) and toLowerCase ( ) return a string with altered case.
• charAt ( ) returns a character by position, facilitating examination of strings; charCodeAt ( ) returns the numerial unicode value of a character by position.
• indexOf ( ) returns the index of the first occurrence of the argument in a string. e.g., "JavaScript".indexOf("S") returns 4; -1 is returned if the argument is not found in the string.
• lastIndexOf ( ) returns the index of the last occurence of the argument in a string.
• substring (startIndex, endIndex) is used to extract substrings, beginning with index startIndex and ending with endIndex. Slice ( ) is similar, but permits negative arguments, which are treated as offsets from the end of the string.

Manipulating strings: Concatenation with the + operator or the String.concat( ) method joins strings. Split (stringArg) returns an array of strings based on a delimiter stringArg (e.g., "," for a comma delimiter).

Escaping characters

To insert special characters into a string, they must be preceeded by a back slash ( \ ). These "escaped" characters include

• \' single quote
• \" double quote
• \\ backslash
• \n new line
• \r carriage return (permits overprinting)
• \t tab
• \b backspace (overprint one character)