CODEWITHSUNDEEP
javascriptregex
M.S.Naidu
M.S.Naidu

Reputation: 2289

Validate the string which needs to match particular condition(Regular Expression)?

I want to validate the string, which should not contain any special characters except underscore(_). For that i have written below code but i was not able to get it through.

var string = 'pro$12';
var result = /[a-zA-Z0-9_]*/.test(string);

In the above the given string is not valid but i got the result as a true. Can any body tell what i am doing wrong here?

Upvotes: 1

Views: 54

Answers (1)

thefourtheye
thefourtheye

Reputation: 239443

It returns true because, it is able to match pro. You can see the actual matched string, with the match function, like this.

console.log(string.match(/[a-zA-Z0-9_]*/));
# [ 'pro', index: 0, input: 'pro$12' ]

Even when it doesn't match anything, for example, your input is '$12', then also it will return true. Because, * matches 0 or more characters. So, it matches zero characters before $ in $12. (Thanks @Jack for pointing out)

So, what you actually need is

console.log(/^[a-zA-Z0-9_]*$/.test(string));
# false

^ means beginning of the string and $ means ending of the string. Basically you are telling the RegEx engine that, match a string which has only the characters from the character class, from the beginning and ending of the string.

Note: Instead of using the explicit character class, [a-zA-Z0-9_], you can simply use \w. It is exactly the same as the character class you mentioned.

Quoting from MDN Docs for RegExp,

\w

Matches any alphanumeric character from the basic Latin alphabet, including the underscore. Equivalent to [A-Za-z0-9_].

For example, /\w/ matches 'a' in "apple," '5' in "$5.28," and '3' in "3D."

So, your RegEx can be shortened like this

console.log(/^\w*$/.test(string));

Upvotes: 1

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