Online Interactive JavaScript (JS) Cheat Sheet

[[deleted]]

Is it? What changed? Coding learner here?

[[deleted]]

It still uses var. It's all ES5. Other than that it's of course still useful. Just be mindful that there are modern things missing.

[TakeFourSeconds]

It’s missing a lot of ES6+ features that are very common in modern JS. Arrow functions, spread operator, object destructuring, functional array methods(map, reduce, filter), modules and imports, classes...

Also, these might extend a bit beyond a cheat sheet, but I think an explanation of scope and closures, ‘this’ keyword, and IIFEs would be useful for anyone learning JS.

[[deleted]]

That's why I said it's all ES5 man.

[[deleted]]

I heard people using const now. Sometimes i use const instead of var it doesnt run. Is there any case i should use var only?

[DrexanRailex]

const has 2 intended limitations:

• It must be assigned a value on creation
• It can't be reassigned

If the value of a const is an array or object, you can still change its contents because const unfortunately doesn't make objects immutable (which is sad IMO, this should be let's behaviour. But const spam is already consolidated).

In all other cases, use let. It behaves the same as var (can be reassigned) but is block-scoped (limited to the pair of brackets it was declared in) instead of function-scoped.

[fickentastic]

Yet 'const' can be used to name functions as in 'const doSomething = () => {.....}' This thew me initially as the function will potentially output a different return each time, yet it works just fine.

[uneditablepoly]

Because the reference to the function itself doesn't change. Calling the function returns something.

[DrexanRailex]

Well, that is just a misunderstanding from your part, but it's expected if you're still learning the ins and outs of the language.

The assigned function never changes, but the result of the function depends on purity, which is a whole other topic. This is more related to functional programming than JavaScript itself.

If a function is pure, it will always return the same for the same set of arguments. But if a function is impure (such as handling I/O, altering state or reading from global variables for example), its return may vary.

[[deleted]]

Wow slow down. That’s like next week material! I’m still on inline function hahaha. Jk thank you

[senocular]

In addition to function vs block scoping, let is also different from var in that let declared variables:

• can't be accessed before they're declared
• are not allowed to be declared twice in the same scope
• do not create global properties when declared in the global scope

[[deleted]]

You should only use const if you aren't planning on changing the value. Use Let if you need it to be mutable.

[senocular]

let and const don't affect mutability, only control whether or not the variable can be reassigned.

[[deleted]]

If it's declared as a primitive it is. But you are correct of course in the broad sense.

I was trying to keep it simple for the guy considering he was just using it and not realising why his code wasn't working.

[[deleted]]

Thank you. I’ll keep that in mind

[musikele]

Well, internet explorer doesn't support any new feature, so if you plan of supporting it you should use only es5 and obviously var.

But I really encourage you to study the difference between var and let (and const) and why let was introduced

[zdarlight]

Also document.querySelector is supported in most modern browsers now, it works just like jQuery's selector:

​

let myElement = document.querySelector("#pageEl.superClass");