array.from foreach javascript code example

Example 1: javascript foreach

const avengers = ['thor', 'captain america', 'hulk'];
avengers.forEach((item, index)=>{
	console.log(index, item)
})

Example 2: javascript foreach

var colors = ['red', 'blue', 'green'];

colors.forEach(function(color) {
  console.log(color);
});

Example 3: For-each over an array in JavaScript

/** 1. Use forEach and related */
var a = ["a", "b", "c"];
a.forEach(function(entry) {
    console.log(entry);
});

/** 2. Use a simple for loop */
var index;
var a = ["a", "b", "c"];
for (index = 0; index < a.length; ++index) {
    console.log(a[index]);
}

/**3. Use for-in correctly*/
// `a` is a sparse array
var key;
var a = [];
a[0] = "a";
a[10] = "b";
a[10000] = "c";
for (key in a) {
    if (a.hasOwnProperty(key)  &&        // These checks are
        /^0$|^[1-9]\d*$/.test(key) &&    // explained
        key <= 4294967294                // below
        ) {
        console.log(a[key]);
    }
}

/** 4. Use for-of (use an iterator implicitly) (ES2015+) */
const a = ["a", "b", "c"];
for (const val of a) {
    console.log(val);
}

/** 5. Use an iterator explicitly (ES2015+) */
const a = ["a", "b", "c"];
const it = a.values();
let entry;
while (!(entry = it.next()).done) {
    console.log(entry.value);
}

Example 4: forEach

const arraySparse = [1,3,,7]
let numCallbackRuns = 0

arraySparse.forEach((element) => {
  console.log(element)
  numCallbackRuns++
})

console.log("numCallbackRuns: ", numCallbackRuns)

// 1
// 3
// 7
// numCallbackRuns: 3
// comment: as you can see the missing value between 3 and 7 didn't invoke callback function.

Example 5: javascript foreach

const colors = ['blue', 'green', 'white'];

function iterate(item) {
  console.log(item);
}

colors.forEach(iterate);
// logs "blue"
// logs "green"
// logs "white"

Example 6: array from js

//Array.from() lets you create Arrays from array-like objects
//(objects with a length property and indexed elements);
//and also:

//More clearly, Array.from(obj, mapFn, thisArg)
//has the same result as Array.from(obj).map(mapFn, thisArg), 
//except that it does not create an intermediate array.
//Basically, it's a declaration that overrides the length property of the method
//(so that it has to be used with the same name length),
//setting it with the same value of the given variable. 
//The values are still undefined, it's just a different notation. Take a look:

console.log(Array.from(length, (_,i) => i));
// It doesn't works with non-iterables
// In this case we are passing an integer

console.log(Array.from({LENGTH}, (_,i) => i));
// It doesn't work with a property name different from "length"

console.log(Array.from({length}, (_,i) => i));
// It works because overrides the .length property of the array
// The method Array.from() assumes that the property...
// ...is referring to an iterable (also if not declared) 

console.log(Array.from(Array(length), (_,i) => i));
// This is the demonstration of the above assertion
// In this case we are using a declared array through...
// ...an instance of the straight method Array()...
// ...that accepts an integer as value

//in case any one reads this a got this from er0s in edabit