//variable declaration let varDeclare: string = "Mayank Singh"; //functions function func(num: number = 123): number { return 123; } //arrow function const arrowFunc = (s: string): string => { return ""; }; //void and never could be used as well const oneMethArr: string[] = []; const secMethArr: Array = []; //creating type type typeExample = { name: string; isActive: boolean; }; //return object from a function function version1Obj(): { name: string } { return { name: "mayank" }; } //Just better version of above function version2Obj(user: typeExample): typeExample { return { name: "", isActive: false }; } //some more options typescript provides type moreOptions = { readonly _id: string; //no one can change it anymore name: string; creditCard?: number; //optional stuff, you want to add or not upto you }; //& for combining types, now we have all the features plus some more type combiningTypes = moreOptions & { cvv: number; name: string; }; //can be number or string as per need let twoPossibleOptions: number | string = 2323; //use of typeof for primitives //You can do it like this if you want, that's how union works!! function selectiveTypesWorkflow(id: number | string) { if (typeof id === "string") { id.toLowerCase(); } else { id = id + 2; } } // const data: number[] | string[] = [1, 2, 3]; - all numbers or all strings error const mulitpleArray: (string | number | boolean)[] = [1, "12123", true]; //one more dope use case for making enums!! let onlyThisStuff: "aisle" | "middle" | "window"; //creating tuples let tuplesEx: [string, number, boolean]; tuplesEx = ["hc", 123, true]; //you can always reopen an interface but not types interface Person { readonly dbID: number; random: string; googleId?: string; getSalary: (s: number) => number; //arrow function getCoupon(couponname: string): number; //normal function } //enums are also there //Using and making classes - private, public, protected, readonly //getters and setter are also there //You can extends classes as well class User { //pre mention those variables, like we do in java email: string; private name: string; readonly city: string = ""; //should be empty if not init constructor(email: string, name: string) { this.email = email; this.name = name; } } //You can implement more than one interface in a class //Concept of abstract classes is also there, if you wanna check it bruh //Generics baby interface Bottle { brand: string; type: number; } function identityFour(val: T): T { return val; } identityFour({ brand: "Mayank", type: 123, }); //arrow function generic, really important const getMoreSearchProducts = (prod: T[]): T => { //do some operation const myIndex = 4; return prod[myIndex]; };