Converting String to Numbers
If you have a string and want to convert it to a number then use the parseInt() method. For example this script returns integer values containing 1234 and 43 respectively into X:
X = parseInt("1234",10);
X = parseInt("34abc",10);
The second argument (10) specifies you want to use a base 10 numbering system. It's unusual to use anything for this parameter except 10 and you should always specify it as the default is a bit unpredictable. (See, for example, http://www.w3schools.com/jsref/jsref_obj_global.asp if you are interested as to why)
If you need to have decimals then use parseFloat(). For example this script returns floating point values 1234.345 and 34.7 respectively into X:
X = parseFloat("1234.345");
X = parseFloat("34.7abc");
Remember that these are floating point values so they are not always as accurate or as predictable as signed or packed decimals numbers.