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Things I learnt during my latest Javascript Code Kata

Sometimes I do a code kata at That is a fun way to solve computer science related problems, learn on the way to solve them and especially learn from the solutions of others.

Today I completed the kata “Make a spanning tree” using Javascript. I occasionally use Javascript to write an event handler or so but I don’t have much experience in “modern” Javascript. Here is what I learnt from looking at the solutions of others.


I know this from my Scala class and Clojure.

You can assign array elements to variables:

so “…rest” is assign the rest of the array.

This is nice syntactic sugar also when working with nested arrays. Eg when “edges” is an array of pairs:

There is object destructuring:

and even assigning to new variable names

See MDN web docs for more.

Spread operator to create an array using an array literal

Using an array literal to create an array from two other arrays:

Objects are associative arrays (aka Maps)

Although I already knew this, kind of, this refreshes my JS

First, you can add properties to Objects without declaring them in
the first place:

Second, instead of the dot-notation you can use array index
notation using the property name as the index:

One solution uses this in order to save the weighted edges in an
object just like i did in the proper Map object:

Third, methods are kind of properties, too. In the same solution,
“minOrMaxFunc” is cleverly choosen (“minOrMax” argument is either
“min” or “max”):

it creates an objects with two methods: “min” and “max” and then
accesses the one that is given in the argument. If “minOrMax” is
“min”, a reference of the “min” method is returned.

Strings are arrays

Destructuring works with strings:

and you can index strings:

“var” vs. “let”

Of course, the solutions written in “modern” JS use “let” and
“const” all over the place. I just reassured myself about the
difference between let and var:

First, variables declared in a block using “var” are visible
outside that block and are “known” before being declared:

a block might be a for-loop.

Variables declared using let are not visible outside the block and
are not “known” before declared:

Third, you might not redeclare a variable using let:

So basically, “let” is a sane way to declare variables.

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