Allow only certain character in string. Javascript

Question

I have no idea, why this simple code is not working. I am planning to match a string against the allowed pattern. The string should ONLY have a-z, A-Z, 0-9, _ (underscore), . (dot) , - (hiphen).

Below is code:

var profileIDPattern = /[a-zA-Z0-9_.-]./;
var str = 'Heman%t';
console.log('hemant',profileIDPattern.test(str));

The code logs 'true' for below string, although these string DOES NOT match the pattern.

'Heman%t' -> true
'#Hemant$' -> true

I dont know what is the problem.

Arg0n · Accepted Answer · 2017-06-02 12:15:00Z

6

Try changing it to this RegExp (/^[a-zA-Z0-9_.-]*$/):

var profileIDPattern = /^[a-zA-Z0-9_.-]*$/;
var str1 = 'Hemant-._67%'
var str2 = 'Hemant-._67';
console.log('hemant1',profileIDPattern.test(str1));
console.log('hemant2',profileIDPattern.test(str2));

answered Jun 2, 2017 at 12:15

Arg0n

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5 Comments

Hemant Yadav Over a year ago

Hey thanks @Arg0n, it worked. Can you please help, what does this * means here. If I am not wrong, then ^ and $ means for start and end of string. I think when I tried last time this type of expression, I have not kept * in it.

Arg0n Over a year ago

@HemantYadav It means 'zero or more' of the chars inside []. If you want 'one or more' change it to +. You are correct about ^ and $.

Pavneet_Singh Over a year ago

there is a flaw in your pattern , it will also match empty string , try it ''.test(str1)

Arg0n Over a year ago

@Pavneet_Singh As stated, if he wants 'one or more' change it to +. The question does not mention if empty string is valid or not.

Pavneet_Singh Over a year ago

The question does not mention if empty string is valid or not , so read this carefully by OP

I am planning to match a string against the allowed pattern. The string should ONLY have a-z, A-Z, 0-9, _ (underscore), . (dot) , - (hiphen).

Pavneet_Singh · Accepted Answer · 2017-06-02 12:44:46Z

2

Issues : [a-zA-Z0-9_.-] will match any character inside [] and . will match anything after so basically it will match the mention character and any other character

Use ^ and $ anchor to mention start and end of match and remove .

^[a-zA-Z0-9_.-]+ : starting with any given value inside []

[a-zA-Z0-9_.-]+$ : one or more matches and $ to end the match

var profileIDPattern = /^[a-zA-Z0-9_.-]+$/;

console.log('hemant',    profileIDPattern.test('Heman%t'));    // no match -
console.log('hemant-._', profileIDPattern.test('hemant-._'));  // valid match
console.log('empty',     profileIDPattern.test(''));           // no match ,empty

edited Jun 2, 2017 at 12:44

answered Jun 2, 2017 at 12:15

Pavneet_Singh

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