To convert Map to JSON object in JavaScript, we use the Object.fromEntries method.
For instance, we write
const map1 = new Map([
["foo", "bar"],
["baz", 42],
]);
const obj = Object.fromEntries(map1);
to create a map with the Map constructor.
Then we call Object.fromEntries with map1 to convert it to an array of key-value pair arrays.
To check whether multiple values exist within a JavaScript array, we use the every and includes methods.
For instance, we write
const success = arrayA.every((val) => arrayB.includes(val));
to call arrayA.every with a callback that checks if every val in arrayA is in “arrayBwithincludes`.
If the condition is met for all elements in arrayA, then true is return.
To loop through a set of elements in JavaScript, we use a for-of loop.
For instance, we write
const list = [
{ a: 1, b: 2 },
{ a: 3, b: 5 },
{ a: 8, b: 2 },
{ a: 4, b: 1 },
{ a: 0, b: 8 },
];
for (const item of list) {
console.log(item);
}
to loop through the list array with a for-of loop.
Then we get the item being looped through and log it.
To get array element fulfilling a condition with JavaScript, we call the filter method.
For instance, we write
const isGreaterThanFive = (x) => {
return x > 5;
};
const filtered = [1, 10, 4, 6].filter(isGreaterThanFive);
to call [1, 10, 4, 6].filter with isGreaterThanFive to return an array with the entries that are greater than 5 in the [1, 10, 4, 6] array.
To sort a JavaScript array with arrays in it by string, we call the sort method.
For instance, we write
const comparator = (a, b) => {
if (a[1] < b[1]) return -1;
if (a[1] > b[1]) return 1;
return 0;
};
const myArray = [
[1, "alfred", "..."],
[23, "berta", "..."],
[2, "zimmermann", "..."],
[4, "albert", "..."],
];
const sortedMyArray = myArray.sort(comparator);
to call myArray.sort with the comparator function to sort the array in ascending order by the 2nd entry of each array.
We do the comparison with the comparison operators and return -1 if a[1] comes before b[1].
And we return 1 when a[1] comes after b[1] to sort in ascending order.