How can I return true or false based on a string based expression in JavaScript?

Question

I'm needing to create a dynamic validator based on a string value that's passed into a json object. So let's say you have the following string:

var required: "Homes > 0"

In this example, "Homes" is an accessible object within my function. I want to logically turn the above into:

if (this.Homes > 0) { return true; }

Thinking about this in parts:

if (this[left] > parsed[right]) { return true; }

I think you get the idea. I'm not sure if there's a way to easily extract operators without just doing a switch for every type? As in:

required: "Homes = 0" // this[Left] === 0

I'm about to do this in a very horrifying ugly string splitting way with a switch case on the operators. Was just wondering if there was a super slick way to make something like this robust.

Answer 1

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/eval

eval('Homes > 0');

but please consider using this pattern instead:

function Class(){
     this.validate = function(){
         return true;
     }
}

var x = new Class();
//overload the validate operator
x.validate = function(){
    return false;
}

You want to avoid eval because it is potentially unsafe because it allows for arbitrary code execution.

Answer 2

尝试使用

eval("if (this.Homes > 0) { return true; }");