75 lines
3.0 KiB
Markdown
75 lines
3.0 KiB
Markdown
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# JavaScript and TypeScript
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You can write micro:bit programs in a subset of [TypeScript](https://www.typescriptlang.org), a superset of JavaScript.
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Many micro:bit programs, especially at the beginner's level, are just plain JavaScript. TypeScript introduces class-based
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object-oriented programming, such as:
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```typescript
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class Greeter {
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greeting: string;
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constructor(message: string) {
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this.greeting = message;
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}
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greet() {
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return "Hello, " + this.greeting;
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}
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}
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let greeter = new Greeter("world");
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basic.showString(greeter.greet())
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```
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This site is meant for teaching programming first, and JavaScript second. For this
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reason, we have stayed away from concepts that are specific to JavaScript (for
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example, prototype inheritance), and instead focused on ones common to most
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modern programming languages (for example, loops, lexically scoped variables,
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functions, classes, lambdas).
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We leverage TypeScript's [type inference](http://www.typescriptlang.org/docs/handbook/type-inference.html) so that
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students need not specify types when clear from context.
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## Supported language features
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* top-level code in the file: "Hello world!" really is just `basic.showString("Hello world!")`
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* [basic types](http://www.typescriptlang.org/docs/handbook/basic-types.html)
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* [variable declarations](http://www.typescriptlang.org/docs/handbook/variable-declarations.html): `let`, `const`, and `var`
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* [functions](http://www.typescriptlang.org/docs/handbook/functions.html) with lexical scoping and recursion
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### User-defined types and modules
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* [classes](http://www.typescriptlang.org/docs/handbook/classes.html) with fields, methods and constructors; `new` keyword
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* [enums](http://www.typescriptlang.org/docs/handbook/enums.html)
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* [namespaces](http://www.typescriptlang.org/docs/handbook/namespaces.html) (a form of modules)
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### Control-flow constructs
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* `if ... else if ... else` statements
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* `while` and `do ... while` loops
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* `for(;;)` loops (see below about `for ... in/of`)
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* `break/continue`; also with labeled loops
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* `switch` statement (on numbers only)
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* `debugger` statement for breakpoints
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### Expressions
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* conditional operator `? :`; lazy boolean operators
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* all arithmetic operators (including bitwise operators); note that in microcontroller targets
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all arithmetic is performed on integers, also when simulating in the browser
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* strings (with a few common methods)
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* [string templates](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals) (`` `x is ${x}` ``)
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* arrow functions `() => ...`
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* array literals `[1, 2, 3]`
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## Unsupported language features
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We generally stay away from the more dynamic parts of JavaScript.
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Things you may miss and we may implement:
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* exceptions (`throw`, `try ... catch`, `try ... finally`)
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* `for ... of` statements
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* object literals `{ foo: 1, bar: "two" }`
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* method-like properties (get/set accessors)
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* class inheritance
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If there is something you'd like to see, please file an issue at [GitHub](http://github.com/microsoft/pxt/issues).
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