在javascript中解析数字比较字符串

Question

So I'm wondering if there is a simple method for, i guess, parsing a string that contains a number comparison.

For example I have a variable that contains a string like this str = "1>3";

Right now I'm using the math plugin to use math.eval(str) which returns a boolean but I feel like this is an awfully big resource to include just for a simple comparison.

My script is currently like this, and I love the simplicity I just hate having to use such a big resource for it.

if (math.eval(str) == true) {
    //do something
} else {
   // do something else
}

Any input on this matter would be greatly appreciated. I thank you in advance.

Answer 1

If you need that for friendly environment (non-public, no security considerations) you can use regular eval to compute result:

var result = eval("1>3");

Note that eval let you run any code and if you let user enter the "condition" and plan to use that for anything outside of personal calculator sample on you local machine - use proper parser that validates expressions and does not use arbitrary functions.

Answer 2

If you have such simple expressions, like

 expression := number comparison_operator number
 comparison_operator := < | > | = | ..

then it is also very simple to write a parser for this.

Eg split the input string along the operator,

"1>3" -> 
op = ">" ->
split: ["1", "3"] -> 
num1_str = "1", num2_str = "3"

convert each number from its string representation to a number value.

num1 = 1, num2 = 3

Then apply the comparison operator.

switch (op) {
case "<":
  return num1 < num2;
case ">":
  return num1 > num2;
case "=":
  return num1 == num2;
// <=, >=, !=, ..
default:
  // unknown operator
}

Answer 3

这个库为表达式解析做了很多开箱即用的事情。