To get first N number of elements from an array with JavaScript, we use the slice method.
For instance, we write
const slicedArray = array.slice(0, n);
to call array.slice with 0 and n to return the first n items in the array array in a new array.
To access and process nested objects, arrays, or JSON with JavaScript, we use object methods.
For instance, we write
const obj = {
a: 1,
b: 2,
c: 3,
};
console.log(Object.keys(obj));
console.log(Object.values(obj));
console.log(Object.entries(obj));
to call Object.keys to get the property keys of obj in an array.
We call Object.values to get the property values of obj in an array.
And we call Object.entries to get the property key-value pair arrays in obj in an array.
To copy array items into another array with JavaScript, we use the concat function.
For instance, we write
const arrayA = [1, 2];
const arrayB = [3, 4];
const newArray = arrayA.concat(arrayB);
to call arrayA.concat with arrayB to return a new array with arrayA‘s contents with arrayB‘s contents being it.
To determine if JavaScript array contains an object with an attribute that equals a given value, we use the find method,.
For instance, we write
if (vendors.find((e) => e.name === "foo")) {
//...
}
to call find with a function that checks if the name property of the objects in the vendors array has value 'foo'.
If it’s true, then the first object that matches the condition will be returned.
To sort an array of integers with JavaScript, we call the sort method.
For instance, we write
const numArray = [140000, 104, 99];
const sortedNumArray = numArray.sort((a, b) => {
return a - b;
});
to call sort with a callback that returns a - b to sort the `numArray entries in ascending order in a new array and return it.