Here’s a few [tricks](https://hackernoon.com/tagged/tricks) and traps that [javascript](https://hackernoon.com/tagged/javascript) beginners should probably know of. If you’re already an expert, feel free to read this with a knowing look.

![](https://hackernoon.com/hn-images/1*WC-PH1ivPs463Eoe4IENUw.jpeg)

Javascript is just another programming language. What could possibly go wrong ?

#### 1\. Did you ever try to sort an array of numbers ?

Javascript `sort()`uses alphanumeric sort per default.

So `[1,2,5,10].sort()` will output `[1, 10, 2, 5].`

![](https://pbs.twimg.com/media/Cze8oIuWIAAaKTu.jpg:large)

To properly sort an array, you can use `[1,2,5,10].sort((a, b) => a — b)`

Easy solution, provided you knew there was a problem in the first place :)

#### 2\. new Date() is just wonderful

![](https://pbs.twimg.com/media/Czk1IhcWIAANO1g.jpg:large)

`new Date()` can accept:

*   no argument: returns now
*   one argument `x`: returns 1st of january 1970, + x milliseconds. Unix people know why.
*   new Date(1, 1, 1) returns 1901, february , 1. Because you know, the first one means 1 year after 1900, the second one is the **second** month of the year (hence february) — who in his right mind would start indexing a table at indice 1 — , and the third one obviously is the **first** day of the month, so 1 — because sometimes the indices do start at 1 — .
*   Oh, and also new Date(2016, 1, 1) will not add 2016 years to 1900. It will simply represent the year 2016.

![](https://hackernoon.com/images/1*DWw9hINcdIdnnGsowQVB-w.gif)

#### 3\. Replace does not replace

I find it to be a good thing, as I don’t like functions that mutate their input. You also should know that `replace` will only replace the first match:

If you wish to replace all occurences, you can use a regex with `/g` :

"bob".replace(/b/g, 'l') === 'lol' // replace all occurences

#### 4\. Careful with comparisons

Reason: \[1,2,3\] and \[1,2,3\] are two separate arrays. They just happen to contain the same values. They have distinct references and cannot be compared with `===`

#### 5\. Array is no primitive type

To know if your var is an array, you can still use `Array.isArray(myVar)`

#### 6\. Closures

This one makes a well known javascript interview question:

Did you expect it to output 0, 1, 2… ? Do you know why it does not ? How would you fix it ?

Let’s mention two of the possible solutions to this problem:

*   Use `let` instead of `var`. Boom. solved.

> “The difference \[between let and var\] is scoping. `var` is scoped to the nearest function block and `let` is scoped to the nearest _enclosing_ block (both are global if outside any block), which can be smaller than a function block.” ([sourc](http://stackoverflow.com/questions/762011/whats-the-difference-between-using-let-and-var-to-declare-a-variable)e)

*   Alternative: use `bind:`

Greeters.push(console.log.bind(null, i))

There are plenty of other ways to do this. These are only my top-2 choices :)

#### 7\. Speaking about bind

What do you think this will output ?

One point for you if you think this will crash with `Cannot read property 'name' of undefined`

Reason: `greet` is not run with proper context. Again, there are many ways to solve this.

*   I personally like

This way you ensure that `greet` is called with your class instance as context.

*   If you feel like `greet` should never be run out of context, you can also bind it in your class constructor:

*   You should also know that fat arrows ( `=>` ) can be used to preserve the context. This will also work:

although I find this last example less elegant in our case.

![](https://hackernoon.com/hn-images/1*xq8btqt6UqtGmqc4dQyQ4A.jpeg)

I’m glad we fixed this

#### Conclusion

Congrats, you’re now able to put stuff on the internet. Probably. Perhaps even without breaking everything (generally it does, though). Cheers \\o/

Let me know if there’s anything I should have mentioned!

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