This is a continuation to my earlier article : 4 JavaScript tips for shorter code

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1. Replace Switch or If-Else with key value pairs

The switch statement and if-else statement evaluates an expression and executes statements associated with that case. But as the number of cases increases the code grows as well.

function returnDaySwitch(val) {
      switch (val) {
         case 1:
            return "It's monday";
         case 2:
            return "It's tuesday";
         case 3:
            return "It's wednesday";
         case 4:
            return "It's thursday";
         case 5:
            return "It's friday";
         case 6:
            return "It's saturday";
         case 7:
            return "It's sunday";
         default:
            return "Enter a value between 1 - 7";
      }
   }
function returnDayIfElse(val) {
    if(val==1){
        return "It's monday";
    }else if(val==2){
        return "It's tuesday";
    }else if(val==3){
        return "It's wednesday";
    }else if(val==4){
        return "It's thursday";
    }else if(val==5){
        return "It's friday";
    }else if(val==6){
        return "It's saturday";
    }else if(val==7){
        return "It's sunday";
    }else{
        return "Enter a value between 1 - 7";
    }
}
const day = 3;
console.log(returnDaySwitch(day)); //It's wednesday
console.log(returnDayIfElse(day)); //It's wednesday

This can be made simpler by using key-value pairs of an object.

function returnDayKeyValue(val) {
    const returnDayObject = {
        1: "It's monday",
        2: "It's tuesday",
        3: "It's wednesday",
        4: "It's thursday",
        5: "It's friday",
        6: "It's saturday",
        7: "It's sunday",
    }
    if(!returnDayObject[val]){
     return "Enter a value between 1 - 7";
    }
    return returnDayObject[val]
}
const day = 3;
console.log(returnDayKeyValue(day)); //It's wednesday

or

const dayToString = day =>
    ({
        1: "It's Monday",
        2: "It's Tuesday",
        3: "It's Wednesday",
        4: "It's Thursday",
        5: "It's Friday",
        6: "It's Saturday",
        7: "It's Sunday",
    }[day] ?? "Enter a value between 1 - 7");

2. Remove duplicate elements in an array

Duplicate elements in an array can be removed by Set constructor and spread syntax. Set constructor converts an array into a set which cannot have duplicate elements. Spread syntax can be used to convert the set object back to an array.

const array = [1,2,2,3,4,5]
const uniq = [...new Set(array)];
console.log(uniq) // [1,2,3,4,5]

3. Computed property names

You cannot set object keys as variables directly. It will read the variable names as key names

const key1 = "name";
const key2 = "age";
const student = {
    key1:"john Doe",
    key2:26
}
console.log(student)
//{ key1:"john Doe", key2:26 }

Starting with ECMAScript 2015, you can put an expression in brackets [], that will be computed and used as the property name.

const key1 = "name";
const key2 = "age";
const student = {
    [key1]:"john Doe",
    [key2]:26
}
console.log(student)
//{ name:"john Doe", age:26 }

4. Prevent falsey value from evaluating to false

There are six falsey values in JavaScript: undefined, null, NaN, 0, "" (empty string), and false. A falsy value is something which evaluates to FALSE, for instance when checking a variable. There could be scenarios where you wont want any falsy value to evaluate to false.

const number = 5;
if(number){
    console.log('The number exists')
}else{
    console.log('The number do not exist')
}

Will print The number exists. But

const number = 0;
if(number){
    console.log('The number exists')
}else{
    console.log('The number do not exist')
}

Will print The number do not exists. This can be handled by giving an exception at the evaluation

const number = null;
if(number===0?true:number){
    console.log('The number exists')
}else{
    console.log('The number do not exist')
}

Will print The number exists. 0 at the expression can be changed with any of the falsy values.