regex in javascript - variable inside regex

Question

Basically i want to return an error if the value of a field is non-numeric or less than a defined minimum length (from array). i'm struggling to get this javascript to work:

var fields = new Array("field_1","field_2","field_3");
var length = new Array(12,4,3);
for (i=0; i < fields.length; i++) {
    var regex = "/^[\d]{" + min_length[i] + "}$/";   //
var field = document.getElementById(numeric_fields[i]);
if (!regex.test(field.value)) {
        alert("error");
    }
    else {
        --do other stuff--
    }
}

ShiningRay · Accepted Answer · 2011-04-23 07:36:39Z

2

Please refer to RegExp class(http://www.regular-expressions.info/javascript.html):

var regex = new RegExp("^\d{1,"+min_length[i] + ",}$");

edited Apr 23, 2011 at 7:36

answered Apr 23, 2011 at 4:15

ShiningRay

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4 Comments

toop Over a year ago

hmm.. var regex = new RegExp("/^[\d]{" + min_length[i] + "}$/"); doesn't seem to work?

ShiningRay Over a year ago

{n} means exactly n matches, so to validate less than a specific length should use {n,}, pay attention to the comma.

ShiningRay Over a year ago

Sorry, it should be {n,m} m means max length

user123444555621 Over a year ago

You need to remove the slashes. Use regex.toString() to check the result.

Eli · Accepted Answer · 2011-04-23 04:41:39Z

Regular expressions can be handy for a lot of things, but for simpler tasks they are not the most efficient way. How about determining if the field is not a number and is of a certain length:

var fields = ["field_1", "field_2", "field_3"];
var length = [12, 4, 3];
for (var i = 0, len = fields.length; i < len; i++) {
    var field = document.getElementById(numeric_fields[i]);
    var value = field.value;
    if (isNaN(field.value) || field.value.toString().length < min_length[i]) {
        alert("error");
    } else {
        // do other stuff
    }
}

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