Category: JavaScript Answers

To use reduce() to find min and max values with JavaScript, we use the spread operator.

For instance, we write

const min = Math.min(...items);
const max = Math.max(...items);

to call Math.min with the values in the items array spread as arguments to get the min value in the items array.

And we call Math.max with the values in the items array spread as arguments to get the max value in the items array.

To set all values of an array with JavaScript, we use the fill method.

For instance, we write

const arr = new Array(3).fill(9);

to create an empty array with length 3 with Array(3).

Then we call fill with 9 to fill the empty slots with 9’s.

To slice an object in JavaScript, we use the Object.entries and Object.fromEntries methods.

For instance, we write

const obj = {
  0: "zero",
  1: "one",
  2: "two",
  3: "three",
  4: "four",
};
const res = Object.fromEntries(Object.entries(obj).slice(0, 4));

to call Object.entries with obj to return an array of key-value pair arrays in obj.

Then we call slice to return a slice of the key-value pair array we want.

And then we call Object.fromEntries with the sliced array to convert it back to an object.

To filter and delete filtered elements in an array with JavaScript, we use the splice and findIndex methods.

For instance, we write

const a = [{ name: "tc_001" }, { name: "tc_002" }, { name: "tc_003" }];
a.splice(
  a.findIndex((e) => e.name === "tc_001"),
  1
);

to call a.findIndex with a callback that checks if name is 'tc_001' in the object being looped through to get the index with name property equal to ‘tc_001’ina`.

Then we call splice with the index and 1 to remove the item in a with such condition.

To create array from for loop with JavaScript, we use the fill and map methods.

For instance, we write

const yearStart = 2000;
const yearEnd = 2040;
const years = Array(yearEnd - yearStart + 1)
  .fill()
  .map((_, i) => yearStart + i);

to create an array with length yearEnd - yearStart + 1 with Array.

Then we call fill to fill the empty slots with undefined.

And then we call map with a callback to map the undefined values to yearStart + i where i is the index of the array currently being looped through.