65 lines
1.8 KiB
Markdown
65 lines
1.8 KiB
Markdown
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# JavaScript Block
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JavaScript is a very powerful language; so powerful that some concepts in
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JavaScript can't be shown using blocks. When PXT encounters a piece of code
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that can't be converted into blocks, it instead creates a grey JavaScript block
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to preserve it. These blocks get converted right back into the original
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JavaScript when you switch back to the text editor.
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```blocks
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for (let index = 0; index <= 5; index++) {
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basic.showNumber(fibonacci(index))
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}
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function fibonacci(n: number): number {
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if (n === 0 || n === 1) {
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return 1;
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}
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return fibonacci(n - 1) + fibonacci(n - 2);
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}
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```
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The code in JavaScript blocks cannot be edited, but the blocks
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themselves can be moved, copied, pasted, and deleted just like any
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other block.
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## How do I get my JavaScript code to convert without any grey blocks?
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The easiest way to write code that will convert cleanly back to blocks
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is to write the code using blocks and convert it to JavaScript. Many blocks
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have a very specifc structure to their JavaScript that must be
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followed in order to have them convert properly. If you have a
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piece of your code that does not convert, try looking at the block
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you were expecting and the JavaScript it produces.
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For example, a for-loop must have this structure to convert to a block:
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```typescript
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for (let x = 0; x <= 5; x++) {
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}
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```
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The following examples can't be represented by the blocks:
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```typescript
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// Condition must be either < or <= with a variable on the left side
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for (let x = 0; x > -1; x++) {
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}
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// The variable in the condition and incrementor must be the declared variable
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for (let x = 0; x <= 5; y++) {
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}
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// The declared variable must be initialized to 0
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for (let x = 2; x <= 5; x++) {
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}
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// All three parts of the for-loop must be present
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for (;;) {
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}
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```
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Try to match the JavaScript of the desired block as closely as
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possible.
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