javascript: best way to check if element exists in pre populated collection?

Question

We are creating a function that would return true if input passed is in certain pre-defined values:

function isEligbile(input){
    return (input == 1 || input == 24 || input == 17);
}

OR

function isEligbile(input){
   var eligibleInputs = {1: true, 24: true, 17: true};
   return eligibleInputs[input]; 
}

I have just mentioned 3 eligible inputs but list is too long. Which is best approach to do such comparison?

Answer 1

You don't need an object literal to store your values, just an array from which you can check for authorized values with indexOf() :

function isEligible(input){
   var eligibleInputs = [1, 24, 17];
   return eligibleInputs.indexOf(input) != -1;
}

Please note that in your case the object literal is not a bad choice. It may be longer to write but also faster in execution.

Answer 2

If you are sure about wanting to hardcode the eligible inputs, I would suggest:

function isEligible(input) {
    var eligibleInputs = [1, 17, 24];
    return eligibleInputs.includes(input);
}

However, if the list of eligible inputs is really long or subject to change, you might want to consider using a different solution, like loading the list from an external source.

The reason I find the snippet above to be a better solution than OPs code is because

• It is easier to expand this list (less characters to type)
• It is a lot more elegant than having an if-statement with an option for every single element
• You can easily iterate over the array if needed for other things

Note: The function in your code is called 'isEligbile' instead of 'isEligible', you might want to fix this.