Question

I am complete novice at regex and Javascript. I have the following problem: need to check into a textfield the existence of one (1) or many (n) consecutive * (asterisk) character/characters eg. * or ** or *** or infinite (n) *. Strings allowed eg. *tomato or tomato* or **tomato or tomato** or as many(n)*tomato many(n)*. So, far I had tried the following:

var str = 'a string'
var value = encodeURIComponent(str);
var reg = /([^\s]\*)|(\*[^\s])/;

if (reg.test(value) == true ) {
    alert ('Watch out your asterisks!!!')
}

Answer 1

By your question it’s hard to decipher what you’re after… But let me try:

Only allow asterisks at beginning or at end

If you only allow an arbitrary number (at least one) of asterisks either at the beginning or at the end (but not on both sides) like:

• *****tomato
• tomato******
• but not **tomato*****

Then use this regular expression:

reg = /^(?:\*+[^*]+|[^*]+\*+)$/;

Match front and back number of asterisks

If you require that the number of asterisks at the biginning matches number of asterisks at the end like

• *****tomato*****
• *tomato*
• but not **tomato*****

then use this regular expression:

reg = /^(\*+)[^*]+\1$/;

Results?

It’s unclear from your question what the results should be when each of these regular expressions match? Are strings that test positive to above regular expressions fine or wrong is on you and your requirements. As long as you have correct regular expressions you’re good to go and provide the functionality you require.

I’ve also written my regular expressions to just exclude asterisks within the string. If you also need to reject spaces or anything else simply adjust the [^...] parts of above expressions.

Note: both regular expressions are untested but should get you started to build the one you actually need and require in your code.