We Keep Coding

How would I change this code to a different format? (Javascript)

The code below is the code that I have written:
function singer(artist) {
var songs = [];
for(var i = 0; i < music.length;i++ ){
if(music[i].artist.indexOf(artist) > -1) {
songs.push(music[i].name);
}
}
return songs;
}
The code that I want to look similar to the function singer(artist) code is this:
const genreCount = () => {
const genres = music.reduce((result, cur) => {
cur.genres.forEach(g => {
if (result.hasOwnProperty(g)) {
result[g] += 1;
}
else
result[g] = 1;
});
return result;
}, {});
return genres;
}
I am unfamiliar with this type of format in Javascript, how would I change it so that const genreCount will look like function singer(artist).

This is what you will get if you want to change that function:
function genreCount() {
const genres = music.reduce(function(result, cur) {
cur.genres.forEach(function(g) {
if (result.hasOwnProperty(g)) {
result[g] += 1;
}
else
result[g] = 1;
});
return result;
}, {});
return genres;
}
or (if you want to assign that fucntion to a const anyway):
const genreCount = function() {
const genres = music.reduce(function(result, cur) {
cur.genres.forEach(function(g) {
if (result.hasOwnProperty(g)) {
result[g] += 1;
}
else
result[g] = 1;
});
return result;
}, {});
return genres;
}
You just should replace arrow functins with the regular function expressions. But I don't know why do you need that.

this style is called functional programming
const singer = artist => music.filter(m => artist.indexOf(m.artist) > -1).map(m => m.name)
here is a good interactive tutorial if you are interested
Functional Programming in Javascript
UPDATE:
oops, sorry for misunderstanding your questions
here is genreCount rewritten with for-loop:
function genreCount(){
const genres = {};
for(var i=0; i<music.length; i++){
var g = music[i]
if (genres.hasOwnProperty(g)) {
genres[g] += 1;
}
else{
genres[g] = 1;
}
}
return genres;
}

Accessing 'this' inside JS iterator's next() method? [duplicate]

This question already has an answer here:
Is there a way to have lexical `this` in methods using the ES6 shorthand method notation?
(1 answer)
Closed 4 years ago.
I'm currently working on a Eloquent JavaScript's object assignments and I'm wondering if there is any way that I can use this inside iterator's next() method (see the code)
class Group {
constructor() {
this.members = [];
}
add(member) {
if (this.has(member)) return;
this.members.push(member);
}
delete(member) {
if (!this.has(member)) return;
this.members.splice(this.members.indexOf(member), 1);
}
has(member) {
return this.members.indexOf(member) !== -1
}
static from(iterable) {
const group = new Group();
for (const element of iterable) {
group.add(element);
}
return group;
}
[Symbol.iterator]() {
let current = 0;
let last = this.members.length - 1;
const that = this;
return {
next() {
if (current <= last) {
return {
done: false,
value: that.members[current++]
}
} else return { done:true }
}
}
}
}
for (let value of Group.from(["a", "b", "c"])) {
console.log(value);
}
As you can see there I'm using this weird const that = this pattern. Is there any way I can get rid of it? Besides using arrow function and extracting iterator to a separate class, as suggested in the solution.

The sortest way, could be an implementation of a default iterator of the object in the constructor section and use yield* expression for delegating to another generator of the array this.members.
constructor() {
this.members = [];
this[Symbol.iterator] = function* () {
yield* this.members;
}
}
class Group {
constructor() {
this.members = [];
this[Symbol.iterator] = function* () {
yield* this.members;
}
}
add(member) {
if (this.has(member)) return;
this.members.push(member);
}
delete(member) {
if (!this.has(member)) return;
this.members.splice(this.members.indexOf(member), 1);
}
has(member) {
return this.members.indexOf(member) !== -1
}
static from(iterable) {
const group = new Group();
for (const element of iterable) {
group.add(element);
}
return group;
}
}
for (let value of Group.from(["a", "b", "c"])) {
console.log(value);
}
.as-console-wrapper { max-height: 100% !important; top: 0; }

you can use the arrow function
class Group {
constructor() {
this.members = [];
}
add(member) {
if (this.has(member)) return;
this.members.push(member);
}
delete(member) {
if (!this.has(member)) return;
this.members.splice(this.members.indexOf(member), 1);
}
has(member) {
return this.members.indexOf(member) !== -1
}
static from(iterable) {
const group = new Group();
for (const element of iterable) {
group.add(element);
}
return group;
}
[Symbol.iterator]() {
let current = 0;
let last = this.members.length - 1;
return {
next: () => {
if (current <= last) {
return {
done: false,
value: this.members[current++]
}
} else return { done:true }
}
}
}
}
for (let value of Group.from(["a", "b", "c"])) {
console.log(value);
}

Getting nested obj value

Given the following obj:
var inputMapping = {
nonNestedItem: "someItem here",
sections: {
general: "Some general section information"
}
};
I'm writing a function to get that data by passing in a string "nonNestedItem" or in the nested case "sections.general". I'm having to use an eval and I was wondering if there was maybe a better way to do this.
Here is what I have so far and it works okay. But improve!
function getNode(name) {
var n = name.split(".");
if (n.length === 1) {
n = name[0];
} else {
var isValid = true,
evalStr = 'inputMapping';
for (var i=0;i<n.length;i++) {
evalStr += '["'+ n[i] +'"]';
if (eval(evalStr) === undefined) {
isValid = false;
break;
}
}
if (isValid) {
// Do something like return the value
}
}
}
Linky to Jsbin

You can use Array.prototype.reduce function like this
var accessString = "sections.general";
console.log(accessString.split(".").reduce(function(previous, current) {
return previous[current];
}, inputMapping));
Output
Some general section information
If your environment doesn't support reduce, you can use this recursive version
function getNestedItem(currentObject, listOfKeys) {
if (listOfKeys.length === 0 || !currentObject) {
return currentObject;
}
return getNestedItem(currentObject[listOfKeys[0]], listOfKeys.slice(1));
}
console.log(getNestedItem(inputMapping, "sections.general".split(".")));

You don't need to use eval() here. You can just use [] to get values from an object. Use a temp object to hold the current value, then update it each time you need the next key.
function getNode(mapping, name) {
var n = name.split(".");
if (n.length === 1) {
return mapping[name];
} else {
var tmp = mapping;
for (var i = 0; i < n.length; i++) {
tmp = tmp[n[i]];
}
return tmp;
}
}

How to put and get the value by the key using object in JavaScript?

How to use the functionality of dictionary in JavaScript?
Look at this question the specified way is working, but I am setting the function instance as a key like this:
Scale = function ()
{
this.Collections = {};
this.IndexTracker = {};
this.UpdateIndex = function ()
{
var index = 0;
for ( var i = 0; i < this.Collections.length; i++ )
{
this.SetIndex( this.Collections[i], index++ );
}
}
this.SetIndex = function ( obj, value )
{
this.IndexTracker[obj] = value;
}
this.GetIndex = function ( obj, value )
{
return this.IndexTracker[obj];
    }
}
this.Collections will hold the some function instance.
The problem here is the function instance is overwritten by the next function instance in this.Collections. The the length of the Collections always is 1. How to solve this?

This is an example:
var Scale = function () {
var _Collections = {},
_IndexTracker = {},
ret = function () {
function UpdateIndex() {
var index = 0,i,l;
for (i = 0,l=_Collections.length; i < l; i++) {
this.SetIndex(_Collections[i], index++);
}
}
function SetIndex(obj, value) {
_IndexTracker[obj] = value;
}
function GetIndex(obj, value) {
return _IndexTracker[obj];
}
return {
UpdateIndex : UpdateIndex,
SetIndex : SetIndex,
GetIndex : GetIndex
};
};
return ret;
}();

Dyanamic Execution of javascript code

I have the following JavaScript:
var djs = function (ob) {
return {
remove: function () { //removes element
if (is_array(ob)) {
for (var i = 0; i < ob.length; i++)
ob[i].parentNode.removeChild(ob[i]);
} else {
ob.parentNode.removeChild(ob);
}
},
empty: function () { //makes element empty
if (is_array(ob)) {
for (var i = 0; i < ob.length; i++)
ob[i].innerHTML = "";
} else {
ob.innerHTML = ""
}
},
html: function (str) { //gets or sets innerHTML
if (str) {
if (is_array(ob)) {
for (var i = 0; i < ob.length; i++)
ob[i].innerHTML = str;
} else {
ob.innerHTML = str;
}
} else {
if (is_array(ob)) {
for (var i = 0; i < ob.length; i++)
rob += ob[i].innerHTML;
return rob;
} else {
return ob.innerHTML;
}
}
}
}
}
Here every time I am checking whether ob is an array or not and executing code. I want to minimize this, like instead of:
if (is_array(ob)) {
for (var i = 0; i < ob.length; i++)
ob[i].parentNode.removeChild(ob[i]);
} else {
ob.parentNode.removeChild(ob);
}
I want to use a function like, doEval(ob,code,return), in this case,
doEval(ob,"parentNode.removeChild("+ob+")",NULL);
"return" parameter will return if I specify any like innerHTML. Can any one help?

Don't repeat is_array check:
var djs=function(ob) {
if (!is_array(ob)) ob = [ob];

#SHiNKiROU is right of course, but just to provide an example of how to solve your problem with higher-order functions:
function doToAll(ob, callback) {
if(is_array(ob)) {
for (var i = 0; i < ob.length; i++) {
callback(ob[i]);
}
} else {
callback(ob);
}
}
...
remove:function(){ //removes element
doToAll(ob, function(actualOb) { actualOb.parentNode.removeChild(actualOb); });
},
...
But again, use #SHiNKiROU:s answer for this particular case.

Try this:
function doEval(a, b, c) {
if(is_array(a)) {
eval(b);
} else {
eval(c);
}
}
NULL doesn't exist by the way, it is null.