- This document focuses on more nuanced topics. It is not comprehensive.
- Examples are taken from MDN mostly
// [@@iterator]() - iterating a string
const str = 'A\uD835\uDC68';
const strIter = str[Symbol.iterator]();
console.log(strIter.next().value); // "A"
console.log(strIter.next().value); // "\uD835\uDC68"
// character codes
const sentence = 'The quick brown fox jumps over the lazy dog.';
sentence.charAt(4); // q
sentence.charCodeAt(4); // 113
'ABC'.codePointAt(0) // 65
'ABC'.codePointAt(0).toString(16) // 41
'😍'.codePointAt(0) // 128525
'\ud83d\ude0d'.codePointAt(0) // 128525
'\ud83d\ude0d'.codePointAt(0).toString(16) // 1f60d
"hello".concat(" ", "world"); // "hello world"
String.fromCharCode(189, 43, 190, 61); // "½+¾="
String.fromCodePoint(9731, 9733, 9842, 0x2F804); // "☃★♲你"
// Misc functions
"Cats are the best!".endsWith("best!"); // true
sentence.includes("fox"); // true
sentence.indexOf("dog"); // 40
sentence.lastIndexOf("the") // 31
// comparing words
'a'.localeCompare('c'); // -1
'check'.localeCompare('against'); // 1
'a'.localeCompare('a'); // 0
let items = ['réservé', 'Premier', 'Cliché', 'communiqué', 'café', 'Adieu'];
items.sort( (a, b) => a.localeCompare(b, 'fr', { ignorePunctuation: true }));
// ['Adieu', 'café', 'Cliché', 'communiqué', 'Premier', 'réservé']
// .match()
sentence.match(/[A-Z]/g); // ["T"];
// .matchall() - must be in new array
[..."test1test2".matchAll(/t(e)(st(\d?))/g)]; // [["test1", "e", "st1", "1"], ["test2", "e", "st2", "2"]]
// .normalize()
const name1 = '\u0041\u006d\u00e9\u006c\u0069\u0065';
name1.normalize('NFC'); // "Amélie, Amélie"
// .padEnd(targetLength, char)
"Breaded Mushrooms".padEnd(25, '.'); // "Breaded Mushrooms........"
// .padStart(targetLength, char)
const fullNumber = '2034399002125581';
const last4Digits = fullNumber.slice(-4);
const maskedNumber = last4Digits.padStart(fullNumber.length, '*'); // "************5581"
// .raw()
// ignore escaped values. Keep template literals
String.raw`C:\Development\profile\aboutme.html` // "C:\Development\profile\aboutme.html"
// .repeat(count)
"hello".repeat(2); // "hello hello"
// .replace(regexp, newSubStr)
// .replace(regexp, replacerFunction)
// .replace(substr, newSubStr)
// .replace(substr, replacerFunction)
// if string, only first occurence is replaced
"have a good day".replace("good", "great"); // "have a great day"
// replaceAll(regexp, newSubstr)
// replaceAll(regexp, replacerFunction)
// replaceAll(substr, newSubstr)
// replaceAll(substr, replacerFunction)
"have a good good day".replaceAll(/good/ig, "great"); // "have a great great day"
// .search(regexp)
sentence.search(/[^\w\s]/g); // 43
// .slice(beginIndex)
// .slice(beginIndex, endIndex)
// does not include the endIndex
sentence.slice(31); // "the lazy dog."
sentence.slice(-4); // "dog."
// .split()
// .startsWith(searchString)
// .startsWith(searchString, position)
"Saturday night plans".startsWith("Sat"); // true
// substring(indexStart)
// substring(indexStart, indexEnd)
// Stick with slice()
"Mozilla".substring(1, 3); // "oz"
"Mozilla".substring(2); // "zilla"
// toLocaleLowerCase()
"İstanbul".toLocaleLowerCase("en-US"); // i̇stanbul
"İstanbul".toLocaleLowerCase("tr"); // istanbul
// toLocaleUpperCase()
// toLowerCase()
// toString()
// toUpperCase()
// trim()
// trimEnd()
" Hello world! ".trimEnd(); // " Hello world!"
// trimStart()
// valueOf()
const stringObj = new String("foo");
stringObj; // String { "foo" }
stringObj.valueOf() // "foo" // .constructor()
let o = {}
o.constructor === Object // true
// .assign()
// does not deep clone
const target = { a: 1, b: 2 };
const source = { b: 4, c: 5 };
const returnedTarget = Object.assign(target, source);
target; // Object { a: 1, b: 4, c: 5 }
returnedTarget; // Object { a: 1, b: 4, c: 5 }
// to deep clone
obj2 = Object.assign({}, obj1);
obj2 = {...obj1};
// .create()
const ability = {
fly: true,
walk: true,
};
const me = Object.create(ability);
me.fly; // true
// .defineProperties()
const object1 = {};
Object.defineProperties(object1, {
property1: {
value: 42,
writable: true
},
property2: {}
});
object1.property1; // 42
// .defineProperty()
const object1 = {};
Object.defineProperty(object1, 'property1', {
value: 42,
writable: false
});
object1.property1 = 77;
object1.property1; // 42
// .entries()
const object1 = {
a: 'somestring',
b: 42
};
for (const [key, value] of Object.entries(object1)) {
console.log(`${key}: ${value}`);
}
// "a: somestring"
// "b: 42"
// .freeze()
// .fromEntries()
const entries = new Map([
['foo', 'bar'],
['baz', 42]
]);
const obj = Object.fromEntries(entries);
obj; // Object { foo: "bar", baz: 42 }
// .getOwnPropertyDescriptor()
o = { bar: 42 };
d = Object.getOwnPropertyDescriptor(o, 'bar');
// d is {
// configurable: true,
// enumerable: true,
// value: 42,
// writable: true
// }
// .getOwnPropertyDescriptors()
// .getOwnPropertyNames()
const object1 = {
a: 1,
b: 2,
c: 3
};
console.log(Object.getOwnPropertyNames(object1));
// expected output: Array ["a", "b", "c"]
// .getOwnPropertySymbols()
const object1 = {};
const a = Symbol('a');
const b = Symbol.for('b');
object1[a] = 'localSymbol';
object1[b] = 'globalSymbol';
const objectSymbols = Object.getOwnPropertySymbols(object1);
console.log(objectSymbols.length);
// expected output: 2
// .getPrototypeOf()
const prototype1 = {};
const object1 = Object.create(prototype1);
console.log(Object.getPrototypeOf(object1) === prototype1);
// expected output: true
// .hasOwnProperty()
const object1 = {};
object1.property1 = 42;
console.log(object1.hasOwnProperty('property1'));
// expected output: true
// is()
// Case 1: Evaluation result is the same as using ===
Object.is(25, 25); // true
Object.is('foo', 'foo'); // true
Object.is('foo', 'bar'); // false
Object.is(null, null); // true
Object.is(undefined, undefined); // true
Object.is(window, window); // true
Object.is([], []); // false
const foo = { a: 1 };
const bar = { a: 1 };
Object.is(foo, foo); // true
Object.is(foo, bar); // false
// Case 2: Signed zero
Object.is(0, -0); // false
Object.is(+0, -0); // false
Object.is(-0, -0); // true
Object.is(0n, -0n); // true
// Case 3: NaN
Object.is(NaN, 0/0); // true
Object.is(NaN, Number.NaN) // true
// isExtensible()
const object1 = {};
console.log(Object.isExtensible(object1));
// expected output: true
Object.preventExtensions(object1);
console.log(Object.isExtensible(object1));
// expected output: false
// isFrozen()
// isPrototypeOf()
// isSealed()
const sealed = {};
Object.seal(sealed);
Object.isSealed(sealed); // === true
// keys()
const object1 = {
a: 'somestring',
b: 42,
c: false
};
console.log(Object.keys(object1));
// expected output: Array ["a", "b", "c"]
// preventExtensions()
// Cannot add new properties to the object
const object1 = {};
Object.preventExtensions(object1);
try {
Object.defineProperty(object1, 'property1', {
value: 42
});
} catch (e) {
console.log(e);
// expected output: TypeError: Cannot define property property1, object is not extensible
}
// propertyIsEnumerable()
// seal()
// Prevents new properties to be writtent to the object
// setPrototypeOf()
// toLocaleString()
const date1 = new Date(Date.UTC(2012, 11, 20, 3, 0, 0));
console.log(date1.toLocaleString('ar-EG'));
// expected output: "٢٠/١٢/٢٠١٢ ٤:٠٠:٠٠ ص"
const number1 = 123456.789;
console.log(number1.toLocaleString('de-DE'));
// expected output: "123.456,789"
// toString()
// valueOf()
+"5" // 5 (string to number)
+"" // 0 (string to number)
+"1 + 2" // NaN (doesn't evaluate)
+new Date() // same as (new Date()).getTime()
+"foo" // NaN (string to number)
+{} // NaN
+[] // 0 (toString() returns an empty string list)
+[1] // 1
+[1,2] // NaN
+new Set([1]) // NaN
+BigInt(1) // Uncaught TypeError: Cannot convert a BigInt value to a number
+undefined // NaN
+null // 0
+true // 1
+false // 0
// values()
const object1 = {
a: 'somestring',
b: 42,
c: false
};
console.log(Object.values(object1));
// expected output: Array ["somestring", 42, false]