Bellow, I will explain you some popular JavaScript mistakes
Use const/let instead of var
Replace old fashioned var with new const, that will guarantee you better condition of your code.
// bad
var a = ‘foo’
var b = ‘bar’
// good
const a = ‘foo’
const b = ‘bar’
If you really need to change variable use let, it’s like var but let has block range, var has functional range.
What is block variable?
Block variable you can read only in defined block of code where was defined.
for(let i = 0; i < 10; i++) {
let j = 10
console.log(j)
//variable j range
}
console.log(j) //ReferenceError: i is not defined
Functional variable you can read inside whole function not only in the code block.
for(let i = 0; i < 10; i++) {
var j = 10
console.log(j) // 10
}
console.log(j) //10
Both let and const are in block range.
Use Template Literals
Manually joining string with + it’s terrible, it’s bad for refactoring and code readability. The best way for joining words is Template Literals.
If you earlier joined words like that, read this chapter.
const name = ‘Maciej’
console.log(‘Hello ‘+ name + ‘, wave’)
Now I’ll compare the old method with Template Literals.
const name = ‘Maciej’
console.log(`Hello ${name}, wave`)
It’s more clear, right?
In Template Literals you can easily add new lines with only just enter button.
const name = ‘Maciej’
console.log(`Hello ${name}
,wave`)
Copy array with spread operator
I think every one of us sometimes must copy the array, but only half of us know about spread operator.
const array = [1,2,3,4,5]
//bad
const newArray = []
for(let i = 0; i < array.length; i++){
newArray[i] = array[i]
}
//good
const newArray = [...array]
Conditional operators
Every one of us sometimes must or want to use conditional operators from some reasons, sometimes you want to save a couple of lines or make the code cleaner.
const a = 0
let b = 0
!a ? b = 1 : b = 2
Like you see on the above snippet, this is not perfect code it's looks weird.
Below you will see easier way.
b = !a ? 1 : 2
Tadam! Looks better, right?
Thanks for reading 🙏
Changelog:
07/22/2020
Added:
Use const/let instead of var
Use Template Literals
Copy array with spread operator
Conditional operator
If you like this article, please follow me on Twitter @MaciejDEV
Photo by NeONBRAND on Unsplash
Top comments (4)
Nice thank you
You have also :
Regards
Thank you for your attention!
I once intentionally used a var declaration at a C style for loop so the value would be accessible from the outside and I got a React warning asking me not to do it. I went quickly from "I'm a genius!" to "Ima refactor dis..." ):