This really is a must read for any JavaScript developer. I have written this guide to shorthand JavaScript coding techniques that I have picked up over the years. To help you understand what is going on, I have included the longhand versions to give some coding perspective.
August 26th, 2019: This article was updated to add new shorthand tips based on the latest specifications. If you want to learn more about ES6 and beyond, sign up for SitePoint Premium and check out our extensive library of modern JavaScript resources.
1. The Ternary Operator
This is a great code saver when you want to write an if..else statement in just one line.
Longhand:
const x = 20;
let answer;
if (x > 10) {
answer = "greater than 10";
} else {
answer = "less than 10";
}
Shorthand:
const answer = x > 10 ? "greater than 10" : "less than 10";
You can also nest your if statement like this:
const answer = x > 10 ? "greater than 10" : x < 5 ? "less than 5" : "between 5 and 10";
2. Short-circuit Evaluation Shorthand
When assigning a variable value to another variable, you may want to ensure that the source variable is not null, undefined, or empty. You can either write a long if statement with multiple conditionals, or use a short-circuit evaluation.
Longhand:
if (variable1 !== null || variable1 !== undefined || variable1 !== '') {
let variable2 = variable1;
}
Shorthand:
const variable2 = variable1 || 'new';
Don’t believe me? Test it yourself (paste the following code in es6console):
let variable1;
let variable2 = variable1 || 'bar';
console.log(variable2 === 'bar'); // prints true
variable1 = 'foo';
variable2 = variable1 || 'bar';
console.log(variable2); // prints foo
Do note that if you set variable1 to false or 0, the value bar will be assigned.
3. Declaring Variables Shorthand
It's good practice to declare your variable assignments at the beginning of your functions. This shorthand method can save you lots of time and space when declaring multiple variables at the same time.
Longhand:
let x;
let y;
let z = 3;
Shorthand:
let x, y, z=3;
4. If Presence Shorthand
This might be trivial, but worth a mention. When doing “if checks”, assignment operators can sometimes be omitted.
Longhand:
if (likeJavaScript === true)
Shorthand:
if (likeJavaScript)
Note: these two examples are not exactly equal, as the shorthand check will pass as long as
likeJavaScriptis a truthy value.
Here is another example. If a is NOT equal to true, then do something.
Longhand:
let a;
if ( a !== true ) {
// do something...
}
Shorthand:
let a;
if ( !a ) {
// do something...
}
5. JavaScript For Loop Shorthand
This little tip is really useful if you want plain JavaScript and don't want to rely on external libraries such as jQuery or lodash.
Longhand:
const fruits = ['mango', 'peach', 'banana'];
for (let i = 0; i < fruits.length; i++)
Shorthand:
for (let fruit of fruits)
If you just wanted to access the index, do:
for (let index in fruits)
This also works if you want to access keys in a literal object:
const obj = {continent: 'Africa', country: 'Kenya', city: 'Nairobi'}
for (let key in obj)
console.log(key) // output: continent, country, city
Shorthand for Array.forEach:
function logArrayElements(element, index, array) {
console.log("a[" + index + "] = " + element);
}
[2, 5, 9].forEach(logArrayElements);
// a[0] = 2
// a[1] = 5
// a[2] = 9
6. Short-circuit Evaluation
Instead of writing six lines of code to assign a default value if the intended parameter is null or undefined, we can simply use a short-circuit logical operator and accomplish the same thing with just one line of code.
Longhand:
let dbHost;
if (process.env.DB_HOST) {
dbHost = process.env.DB_HOST;
} else {
dbHost = 'localhost';
}
Shorthand:
const dbHost = process.env.DB_HOST || 'localhost';
7. Decimal Base Exponents
You may have seen this one around. It’s essentially a fancy way to write numbers without the trailing zeros. For example, 1e7 essentially means 1 followed by 7 zeros. It represents a decimal base (which JavaScript interprets as a float type) equal to 10,000,000.
Longhand:
for (let i = 0; i < 10000; i++) {}
Shorthand:
for (let i = 0; i < 1e7; i++) {}
// All the below will evaluate to true
1e0 === 1;
1e1 === 10;
1e2 === 100;
1e3 === 1000;
1e4 === 10000;
1e5 === 100000;
8. Object Property Shorthand
Defining object literals in JavaScript makes life much easier. ES6 provides an even easier way of assigning properties to objects. If the variable name is the same as the object key, you can take advantage of the shorthand notation.
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by Michael Wanyoike via SitePoint
