Are Variable Operators Possible?

Question

Is there a way to do something similar to either of the following:

var1 = 10; var2 = 20;
var operator = "<";
console.log(var1 operator var2); // returns true

-- OR --

var1 = 10; var2 = 20;
var operator = "+";
total = var1 operator var2; // total === 30

Solution 1

We can implement this using eval, since we are using it for operator checking.

var number1 = 30;
var number2 = 40;
var operator = '===';

function evaluate(param1, param2, operator) {
  return eval(param1 + operator + param2);
}

if (evaluate(number1, number2, operator)) {}

in this way we can use dynamic operator evaluation.

Solution 2

I believe you want a variable operator. here's one, created as object. you can change the current operation by changing:

[yourObjectName].operation = "<" //changes operation to less than


function VarOperator(op) { //you object containing your operator
    this.operation = op;

    this.evaluate = function evaluate(param1, param2) {
        switch(this.operation) {
            case "+":
                return param1 + param2;
            case "-":
                return param1 - param2;
            case "*":
                return param1 * param2;
            case "/":
                return param1 / param2;
            case "<":
                return param1 < param2;
            case ">":
                return param1 > param2;
        }
    }
}

//sample usage:
var vo = new VarOperator("+"); //initial operation: addition
vo.evaluate(21,5); // returns 26
vo.operation = "-" // new operation: subtraction
vo.evaluate(21,5); //returns 16
vo.operation = ">" //new operation: ">"
vo.evaluate(21,5); //returns true

Solution 3

You can use the eval() function, but that is not a good idea. I think the better way is writing functions for your operators like this:

var addition = function(first, second) {
   return first+second;
};

var subtraction = function(first, second) {
   return first-second;
};

var operator = addition;

alert(operator(12, 13));

var operator = subtraction;

alert(operator(12, 13));

Solution 4

A bit newer approach. It can be done pretty decent using currying:

const calculate = a => str => b => {switch(str) {
  case '+': return a + b
  case '-': return a - b
  case '/': return a / b
  case '*': return a * b
  default: return 'Invalid operation'
}}

const res = calculate(15)('*')(28)

console.log('15 * 28 =', res)

Solution 5

You can't overload operators in JavaScript. You can off course use functions to help

var plus = function(a, b) {
    return a + b;
};

var smaller = function(a, b) { 
    return a < b;
};

var operator = plus;
var total = operator(a, b);
operator = smaller;
if(operator(var1, var2)){ /*do something*/ }

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Comments

[karan bhatia]

Thank you!!!!!!!! I like this approach. Much cleaner

[Callam]

Big security risk - developer.mozilla.org/en-US/docs/web/javascript/reference/…!