To get a list of associative array keys with JavaScript, we call the Object.keys method.
For instance, we write
const dictionary = {
cats: [1, 2, 37, 38, 40, 32, 33, 35, 39, 36],
dogs: [4, 5, 6, 3, 2],
};
const keys = Object.keys(dictionary);
console.log(keys);
to call Object.keys with dictionary to return a list of key strings from the dictionary object.
To map and filter an array at the same time with JavaScript, we use the flatMap method.
For instance, we write
const names = options.flatMap((o) => (o.assigned ? [o.name] : []));
to call options.flatMap with a callback that checks if o.assigned is set.
If it is, then we array with o.name inside.
Otherwise, we return an empty array.
And we use flatMap to combine them into one flattened array.
To check if a string contains text from an array of substrings in JavaScript, we can use the some and includes method.
For instance, we write
if (substrings.some((v) => str.includes(v))) {
// ...
}
to call some on the substrings array with a callback that calls str.includes with the v entry being looped through in substrings to check if v is in the str string.
If any value v is in str, then some returns true.
To split a string into segments of n characters with JavaScript, we call the match method.
For instance, we write
const str = "abcdefghijkl";
console.log(str.match(/.{1,3}/g));
to call str.match with a regex the matches groups of 1 to 3 characters in the str array.
To create an empty typed container array with TypeScript, we can declare the type explicitly.
For instance, we write
const arr: Criminal[] = [];
to declare the arr array with the Criminal type.