Get exact match in string using regex and javascript

Question

I'm trying to get an exact match from a given string, and then manipulate that string. I have a rather large calculator program that you can see here: http://www.marcusparsons.com/projects/calculator. There's nothing on the main pages just yet, and the original code is quite long.

The goal has been to implement a feature into the calculator where Math doesn't have to be prefixed to Math objects/methods. It's worked great up until I added a function that allows a user to use the "acosh()" method (and experimental methods) regardless of whether it's implemented in their browser or not (ehem...IE). The problem I run into is that the algorithm I have now wants to replace "acosh" with aMath.cosh()" because it sees "cos" inside of "acosh".

So, when I pass it the string "acosh(1)+cos(pi/3)" it turns into "aMath.cosh(1)+cos(Math.PI/3)".

Edit: The string above should be "acosh(1)+Math.cos(Math.PI/3)".

I'm a newbie at Regular Expressions, and I'm thinking that is where my problem is.

Here's the example code: http://jsfiddle.net/mparson8/2ej5n3u4/4/

var $mathKeywords = ["E", "LN2", "LN10", "LOG2E", "LOG10E", "PI", "SQRT1_2", "SQRT2", "abs", "acos", "asin", "asinh", "atan", "atan2", "atanh", "cbrt", "ceil", "clz32", "cos", "exp", "expm1", "floor", "fround", "hypot", "imul", "log1p", "log10", "log2", "max", "min", "pow", "random", "round", "sin", "sinh", "sqrt", "tan", "tanh", "trunc"];

var $resultVal = "acosh(1)+cos(PI/3)".toLowerCase();
try {
//Iterate over each Math object/method
$.each($mathKeywords, function (i, val) {
    //Convert val within array to a lower case form
    var $lowerKey = val.toLowerCase();
    //The regex pattern I came up with
    var pattern = new RegExp("(^|\\W)" + $lowerKey + "($|\\W)");
    //See if pattern gives a match within $resultVal
    var $location = $resultVal.match(pattern);
    //Math keyword is found
    if ($location != null) {
        //replace the lowercase version of the math keyword with its properly cased version prepended 
        //with Math. i.e. cos becomes Math.cos and pi becomes Math.PI
        $resultVal = $resultVal.replace($lowerKey, "Math." + val);
    }
});
//Set the result element's value to an evaluation of $resultVal
//A better implementation of the eval exists within the calc program
alert($resultVal);
alert(eval($resultVal));
} catch (err) {
alert("Error: Cannot process expression due to " + err + ".");
}

I appreciate any and all help! :)

(^|\W)cos($|\W) does not match acosh; you've correctly added word boundaries, so I'm not sure that's your problem... — mpen
– mpen, Commented Feb 18, 2015 at 23:55
acosh does not belong in the list, because then it would be a part of the Math prototype, and if you try to run "acosh" in IE, you will get an error because it doesn't exist as part of the Math methods. I haven't taken the other experimental methods out yet, because I have just been running tests. — Marcus Parsons
– Marcus Parsons, Commented Feb 19, 2015 at 0:06
Mark, that regular expression is not the same as the one that is returned from the code. If you show an alert for the $location after it's been set $resultVal.match(pattern); you'll see that it returns some extra characters, as well. — Marcus Parsons
– Marcus Parsons, Commented Feb 19, 2015 at 0:08
@MarcusParsons Oh... that's because the \W is matching the punctuation/operators (e.g. regex101.com/r/zH9hH1/1). What you want is a zero-width assertion, or a capturing group. Just replace (^|\\W) and ($|\\W) both with \b (or \\b in the string) e.g. regex101.com/r/pP9pT0/1 — mpen
– mpen, Commented Feb 19, 2015 at 0:11

Halcyon · Accepted Answer · 2015-02-19 00:34:19Z

5

If you want to continue on the path of regular expressions, this seems to work:

var $mathKeywords = ["E", "LN2", "LN10", "LOG2E", "LOG10E", "PI", "SQRT1_2", "SQRT2", "abs", "acos", "asin", "asinh", "atan", "atan2", "atanh", "cbrt", "ceil", "clz32", "cos", "exp", "expm1", "floor", "fround", "hypot", "imul", "log1p", "log10", "log2", "max", "min", "pow", "random", "round", "sin", "sinh", "sqrt", "tan", "tanh", "trunc"];

var $resultVal = "acosh(1)+cos(PI/3)".toLowerCase();
try {
    //Iterate over each Math object/method
    $.each($mathKeywords, function (i, val) {
        //Convert val within array to a lower case form
        var $lowerKey = val.toLowerCase();
        var pattern = new RegExp("\\b" + $lowerKey + "\\b", "g");
        //See if pattern gives a match within $resultVal
        var $location = $resultVal.match(pattern);
        //Math keyword is found
        if ($location != null) {
            //replace the lowercase version of the math keyword with its properly cased version prepended 
            //with Math. i.e. cos becomes Math.cos and pi becomes Math.PI
            $resultVal = $resultVal.replace(pattern, "Math." + val);
        }
    });
    //Set the result element's value to an evaluation of $resultVal
    //A better implementation of the eval exists within the calc program
    console.log($resultVal);
    console.log(eval($resultVal));
} catch (err) {
    alert("Error: Cannot process expression due to " + err + ".");
}

Output:

acosh(1)+Math.cos(Math.PI/3)

(actually its Error: Cannot process expression due to ReferenceError: acosh is not defined. but you get the point)

Changes:

Use \b as a word boundary
Use pattern (with word boundary) in replacement
Use g flag to replace all occurrences.

edited Feb 19, 2015 at 0:34

answered Feb 19, 2015 at 0:28

Halcyon

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5 Comments

deweyredman Over a year ago

no. you will still have hte problem I described above.

deweyredman Over a year ago

Rearrange the list and I think we might have a winner

Halcyon Over a year ago

@deweyredman Your are not correct. The word boundary \b takes care of that. \bcos\b will not match .acos (or .acosh).

Marcus Parsons Over a year ago

Halcyon, that was exactly what I needed. My problem was BOTH the regular expression and what I needed replacing. I feel like it's a Duh! moment. Thank you a ton! :)

Vikas Yadav Over a year ago

This is really a very good answer. This line needs to be highlighted: new RegExp("\\b" + $lowerKey + "\\b", "g");

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