1
let isDone: boolean = false;
2

3
// 编译通过
4
// 后面约定，未强调编译错误的代码片段，默认为编译通过

1
let createdByNewBoolean: boolean = new Boolean(1);
2

3
// Type 'Boolean' is not assignable to type 'boolean'.
4
//   'boolean' is a primitive, but 'Boolean' is a wrapper object. Prefer using 'boolean' when possible.

1
let createdByNewBoolean: Boolean = new Boolean(1);

1
let createdByBoolean: boolean = Boolean(1);

1
let decLiteral: number = 6;
2
let hexLiteral: number = 0xf00d;
3
// ES6 中的二进制表示法
4
let binaryLiteral: number = 0b1010;
5
// ES6 中的八进制表示法
6
let octalLiteral: number = 0o744;
7
let notANumber: number = NaN;
8
let infinityNumber: number = Infinity;

1
var decLiteral = 6;
2
var hexLiteral = 0xf00d;
3
// ES6 中的二进制表示法
4
var binaryLiteral = 10;
5
// ES6 中的八进制表示法
6
var octalLiteral = 484;
7
var notANumber = NaN;
8
var infinityNumber = Infinity;

1
let myName: string = 'Tom';
2
let myAge: number = 25;
3

4
// 模板字符串
5
let sentence: string = `Hello, my name is ${myName}.
6
I'll be ${myAge + 1} years old next month.`;

1
var myName = 'Tom';
2
var myAge = 25;
3
// 模板字符串
4
var sentence = "Hello, my name is " + myName + ".\nI'll be " + (myAge + 1) + " years old next month.";

1
function alertName(): void {
2
    alert('My name is Tom');
3
}

1
let unusable: void = undefined;

1
let u: undefined = undefined;
2
let n: null = null;

1
// 这样不会报错
2
let num: number = undefined;
3
// 这样也不会报错
4
let u: undefined;
5
let num: number = u;

1
let u: void;
2
let num: number = u;
3

4
// Type 'void' is not assignable to type 'number'.

1
let myFavoriteNumber: string = 'seven';
2
myFavoriteNumber = 7;
3

4
// index.ts(2,1): error TS2322: Type 'number' is not assignable to type 'string'.

1
let myFavoriteNumber: any = 'seven';
2
myFavoriteNumber = 7;

1
let anyThing: any = 'hello';
2
console.log(anyThing.myName);
3
console.log(anyThing.myName.firstName);

1
let anyThing: any = 'Tom';
2
anyThing.setName('Jerry');
3
anyThing.setName('Jerry').sayHello();
4
anyThing.myName.setFirstName('Cat');

1
let something;
2
something = 'seven';
3
something = 7;
4

5
something.setName('Tom');

1
let something: any;
2
something = 'seven';
3
something = 7;
4

5
something.setName('Tom');

1
let myFavoriteNumber = 'seven';
2
myFavoriteNumber = 7;
3

4
// index.ts(2,1): error TS2322: Type 'number' is not assignable to type 'string'.

1
let myFavoriteNumber: string = 'seven';
2
myFavoriteNumber = 7;
3

4
// index.ts(2,1): error TS2322: Type 'number' is not assignable to type 'string'.

1
let myFavoriteNumber;
2
myFavoriteNumber = 'seven';
3
myFavoriteNumber = 7;

1
function getLength(something: string | number): number {
2
    return something.length;
3
}
4

5
// index.ts(2,22): error TS2339: Property 'length' does not exist on type 'string | number'.
6
//   Property 'length' does not exist on type 'number'.

1
function getString(something: string | number): string {
2
    return something.toString();
3
}

1
let myFavoriteNumber: string | number;
2
myFavoriteNumber = 'seven';
3
console.log(myFavoriteNumber.length); // 5
4
myFavoriteNumber = 7;
5
console.log(myFavoriteNumber.length); // 编译时报错
6

7
// index.ts(5,30): error TS2339: Property 'length' does not exist on type 'number'.

1
interface Person {
2
    name: string;
3
    age: number;
4
}
5

6
let tom: Person = {
7
    name: 'Tom',
8
    age: 25
9
};

1
interface Person {
2
    name: string;
3
    age: number;
4
}
5

6
let tom: Person = {
7
    name: 'Tom'
8
};
9

10
// index.ts(6,5): error TS2322: Type '{ name: string; }' is not assignable to type 'Person'.
11
//   Property 'age' is missing in type '{ name: string; }'.

1
interface Person {
2
    name: string;
3
    age: number;
4
}
5

6
let tom: Person = {
7
    name: 'Tom',
8
    age: 25,
9
    gender: 'male'
10
};
11

12
// index.ts(9,5): error TS2322: Type '{ name: string; age: number; gender: string; }' is not assignable to type 'Person'.
13
//   Object literal may only specify known properties, and 'gender' does not exist in type 'Person'.

1
interface Person {
2
    name: string;
3
    age?: number;
4
}
5

6
let tom: Person = {
7
    name: 'Tom',
8
    age: 25,
9
    gender: 'male'
10
};
11

12
// examples/playground/index.ts(9,5): error TS2322: Type '{ name: string; age: number; gender: string; }' is not assignable to type 'Person'.
13
//   Object literal may only specify known properties, and 'gender' does not exist in type 'Person'.

1
interface Person {
2
    name: string;
3
    age?: number;
4
    [propName: string]: any;
5
}
6

7
let tom: Person = {
8
    name: 'Tom',
9
    gender: 'male'
10
};

1
interface Person {
2
    name: string;
3
    age?: number;
4
    [propName: string]: string | number;
5
}
6

7
let tom: Person = {
8
    name: 'Tom',
9
    age: 25,
10
    gender: 'male'
11
};
12

13
// 类型“number | undefined”的属性“age”不能赋给“string”索引类型“string | number”。

1
interface Person {
2
    name: string;
3
    age?: number;
4
    [propName: string]: string | number | undefined;
5
}

1
let fibonacci: number[] = [1, 1, 2, 3, 5];

1
let fibonacci: number[] = [1, '1', 2, 3, 5];
2

3
// Type 'string' is not assignable to type 'number'.

1
let fibonacci: number[] = [1, 1, 2, 3, 5];
2
fibonacci.push('8');
3

4
// Argument of type '"8"' is not assignable to parameter of type 'number'.

1
let fibonacci: Array<number> = [1, 1, 2, 3, 5];

1
interface NumberArray {
2
    [index: number]: number;
3
}
4
let fibonacci: NumberArray = [1, 1, 2, 3, 5];

1
function sum() {
2
    let args: number[] = arguments;
3
}
4

5
// Type 'IArguments' is missing the following properties from type 'number[]': pop, push, concat, join, and 24 more.

1
function sum() {
2
    let args: {
3
        [index: number]: number;
4
        length: number;
5
        callee: Function;
6
    } = arguments;
7
}

1
function sum() {
2
    let args: IArguments = arguments;
3
}

1
interface IArguments {
2
    [index: number]: any;
3
    length: number;
4
    callee: Function;
5
}

1
// 使用剩余参数，args 直接就是一个真正的数组
2
function sum(...args: number[]) {
3
    // args 此时是 number[] 类型，可以直接使用 reduce 等数组方法
4
    return args.reduce((a, b) => a + b, 0);
5
}

1
let list: any[] = ['xcatliu', 25, { website: 'http://xcatliu.com' }];

1
// 函数声明（Function Declaration）
2
function sum(x, y) {
3
    return x + y;
4
}
5

6
// 函数表达式（Function Expression）
7
let mySum = function (x, y) {
8
    return x + y;
9
};

1
function sum(x: number, y: number): number {
2
    return x + y;
3
}

1
function sum(x: number, y: number): number {
2
    return x + y;
3
}
4
sum(1, 2, 3);
5

6
// index.ts(4,1): error TS2346: Supplied parameters do not match any signature of call target.
7
function sum(x: number, y: number): number {
8
    return x + y;
9
}
10
sum(1);
11

12
// index.ts(4,1): error TS2346: Supplied parameters do not match any signature of call target.

1
let mySum = function (x: number, y: number): number {
2
    return x + y;
3
};

1
let mySum: (x: number, y: number) => number = function (x: number, y: number): number {
2
    return x + y;
3
};

1
interface SearchFunc {
2
    (source: string, subString: string): boolean;
3
}
4

5
let mySearch: SearchFunc;
6
mySearch = function(source: string, subString: string) {
7
    return source.search(subString) !== -1;
8
}

1
function buildName(firstName: string, lastName?: string) {
2
    if (lastName) {
3
        return firstName + ' ' + lastName;
4
    } else {
5
        return firstName;
6
    }
7
}
8
let tomcat = buildName('Tom', 'Cat');
9
let tom = buildName('Tom');

1
function buildName(firstName?: string, lastName: string) {
2
    if (firstName) {
3
        return firstName + ' ' + lastName;
4
    } else {
5
        return lastName;
6
    }
7
}
8
let tomcat = buildName('Tom', 'Cat');
9
let tom = buildName(undefined, 'Tom');
10

11
// index.ts(1,40): error TS1016: A required parameter cannot follow an optional parameter.

1
function buildName(firstName: string, lastName: string = 'Cat') {
2
    return firstName + ' ' + lastName;
3
}
4
let tomcat = buildName('Tom', 'Cat');
5
let tom = buildName('Tom');

1
function buildName(firstName: string = 'Tom', lastName: string) {
2
    return firstName + ' ' + lastName;
3
}
4
let tomcat = buildName('Tom', 'Cat');
5
let cat = buildName(undefined, 'Cat');

1
function push(array, ...items) {
2
    items.forEach(function(item) {
3
        array.push(item);
4
    });
5
}
6

7
let a: any[] = [];
8
push(a, 1, 2, 3);

1
function push(array: any[], ...items: any[]) {
2
    items.forEach(function(item) {
3
        array.push(item);
4
    });
5
}
6

7
let a = [];
8
push(a, 1, 2, 3);

1
function reverse(x: number | string): number | string | void {
2
    if (typeof x === 'number') {
3
        return Number(x.toString().split('').reverse().join(''));
4
    } else if (typeof x === 'string') {
5
        return x.split('').reverse().join('');
6
    }
7
}

1
function reverse(x: number): number;
2
function reverse(x: string): string;
3
function reverse(x: number | string): number | string | void {
4
    if (typeof x === 'number') {
5
        return Number(x.toString().split('').reverse().join(''));
6
    } else if (typeof x === 'string') {
7
        return x.split('').reverse().join('');
8
    }
9
}

1
值 as 类型

1
<类型>值

1
interface Animal {
2
    name: string;
3
}
4
interface Cat {
5
    name: string;
6
    run(): void;
7
}
8

9
let tom: Cat = {
10
    name: 'Tom',
11
    run: () => { console.log('run') }
12
};
13
let animal: Animal = tom;

1
interface Animal {
2
    name: string;
3
}
4
interface Cat extends Animal {
5
    run(): void;
6
}

1
interface Animal {
2
    name: string;
3
}
4
interface Cat {
5
    name: string;
6
    run(): void;
7
}
8

9
function testAnimal(animal: Animal) {
10
    return (animal as Cat);
11
}
12
function testCat(cat: Cat) {
13
    return (cat as Animal);
14
}

1
interface Cat {
2
    run(): void;
3
}
4
interface Fish {
5
    swim(): void;
6
}
7

8
function testCat(cat: Cat) {
9
    return (cat as any as Fish);
10
}

1
function toBoolean(something: any): boolean {
2
    return something as boolean;
3
}
4

5
toBoolean(1);
6
// 返回值为 1

1
function toBoolean(something) {
2
    return something;
3
}
4

5
toBoolean(1);
6
// 返回值为 1

1
function toBoolean(something: any): boolean {
2
    return Boolean(something);
3
}
4

5
toBoolean(1);
6
// 返回值为 true

1
function getCacheData(key: string): any {
2
    return (window as any).cache[key];
3
}
4

5
interface Cat {
6
    name: string;
7
    run(): void;
8
}
9

10
const tom = getCacheData('tom') as Cat;
11
tom.run();

1
function getCacheData(key: string): any {
2
    return (window as any).cache[key];
3
}
4

5
interface Cat {
6
    name: string;
7
    run(): void;
8
}
9

10
const tom: Cat = getCacheData('tom');
11
tom.run();

1
interface Animal {
2
    name: string;
3
}
4
interface Cat {
5
    name: string;
6
    run(): void;
7
}
8

9
const animal: Animal = {
10
    name: 'tom'
11
};
12
let tom = animal as Cat;

1
interface Animal {
2
    name: string;
3
}
4
interface Cat {
5
    name: string;
6
    run(): void;
7
}
8

9
const animal: Animal = {
10
    name: 'tom'
11
};
12
let tom: Cat = animal;
13

14
// index.ts:12:5 - error TS2741: Property 'run' is missing in type 'Animal' but required in type 'Cat'.