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Support Async/Await based on #12 #125

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Support Async/Await based on #12 #125

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47 changes: 47 additions & 0 deletions src/program/BlockStatement.js
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Original file line number Diff line number Diff line change
Expand Up @@ -176,6 +176,53 @@ export default class BlockStatement extends Node {

super.transpile(code, transforms);

if (transforms.asyncAwait && this.isFunctionBlock && this.parent.async && this.body.length) {
const first = this.body[0];
const last = this.body[this.body.length - 1];
const hasOnlyOneLine = this.body.length === 1;

// TODO refactor :)
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Refactor how? Who wrote this comment?

Better refactor now before merging, as later it will most likely not ever be refactored.

if (this.parent.type === 'FunctionDeclaration') {
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This does not handle FunctionExpressions.

if (hasOnlyOneLine) {
if (first.type === 'ReturnStatement') {
code.insertLeft(first.argument.start, 'Promise.resolve().then(function() { ');
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insertLeft has been replaced by appendLeft.

code.insertLeft(first.end, ' })');
} else {
code.insertLeft(first.start, 'return Promise.resolve().then(function() { ');
code.insertRight(last.end, ' }).then(function() {})');
}
} else {
code.insertLeft(first.start, 'return Promise.resolve()');
code.insertRight(last.end, '.then(function() {})');

for (let i = 0; i < this.body.length; i++) {
const prev = this.body[i - 1];
const cur = this.body[i];
const next = this.body[i + 1];

if (cur.expression.type === 'AwaitExpression') {
code.insertLeft(cur.start, '.then(function() { ');
code.insertRight(cur.end, ' })');
} else {
if (!prev || prev.expression.type === 'AwaitExpression') {
code.insertLeft(cur.start, '.then(function() { ');
}

if (!next || next.expression.type === 'AwaitExpression') {
code.insertRight(cur.end, ' })');
}
}
}
}

} else if (this.parent.type === 'ArrowFunctionExpression') {
// TODO merge with ^
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TODOs should be new issues IMO, and not included in the code.

// wrap the function's body in a promise
code.insertLeft(first.start + 1, 'Promise.resolve().then(function() { return ');
code.insertLeft(last.end, ' })');
}
}

if (this.createdDeclarations.length) {
introStatementGenerators.push((start, prefix, suffix) => {
const assignment = `${prefix}var ${this.createdDeclarations.join(', ')}${suffix}`;
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3 changes: 3 additions & 0 deletions src/program/types/ArrowFunctionExpression.js
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
import Node from '../Node.js';
import CompileError from '../../utils/CompileError.js';
import removeTrailingComma from '../../utils/removeTrailingComma.js';
import AwaitExpression from './AwaitExpression';

export default class ArrowFunctionExpression extends Node {
initialise(transforms) {
Expand All @@ -22,6 +23,7 @@ export default class ArrowFunctionExpression extends Node {
}
code.remove(charIndex, this.body.start);

AwaitExpression.removeAsync(code, transforms, this.async, this.start);
super.transpile(code, transforms);

// wrap naked parameter
Expand All @@ -38,6 +40,7 @@ export default class ArrowFunctionExpression extends Node {
code.prependRight(this.start, 'function ');
}
} else {
AwaitExpression.removeAsync(code, transforms, this.async, this.start);
super.transpile(code, transforms);
}

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19 changes: 14 additions & 5 deletions src/program/types/AwaitExpression.js
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Original file line number Diff line number Diff line change
@@ -1,11 +1,20 @@
import Node from '../Node.js';
import CompileError from '../../utils/CompileError.js';

const noop = () => {};

export default class AwaitExpression extends Node {
initialise(transforms) {
if (transforms.asyncAwait) {
CompileError.missingTransform("await", "asyncAwait", this);
static removeAsync(code, transforms, async, start, callback = noop) {
if (transforms.asyncAwait && async) {
code.remove(start, start + 6);
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Magic number 6 is mysterious here. Better as named variable, or with a comment?

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could this be "async ".length?

callback();
}
super.initialise(transforms);
}

transpile (code, transforms) {
AwaitExpression.removeAsync(code, transforms, true, this.start, () => {
code.insertLeft(this.argument.start, 'return ');
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This handles the expression as though it was a statement. See for example async () => await 1 + await 2.

});

super.transpile(code, transforms);
}
}
2 changes: 2 additions & 0 deletions src/program/types/FunctionDeclaration.js
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
import Node from '../Node.js';
import CompileError from '../../utils/CompileError.js';
import removeTrailingComma from '../../utils/removeTrailingComma.js';
import AwaitExpression from './AwaitExpression';

export default class FunctionDeclaration extends Node {
initialise(transforms) {
Expand All @@ -20,6 +21,7 @@ export default class FunctionDeclaration extends Node {
}

transpile(code, transforms) {
AwaitExpression.removeAsync(code, transforms, this.async, this.start);
super.transpile(code, transforms);
if (transforms.trailingFunctionCommas && this.params.length) {
removeTrailingComma(code, this.params[this.params.length - 1].end);
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25 changes: 25 additions & 0 deletions test/samples/async-await.js
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Original file line number Diff line number Diff line change
@@ -0,0 +1,25 @@
module.exports = [
{
description: 'transpiles await arrow function call',
input: `async () => await a()`,
output: `!function() { return Promise.resolve().then(function() { return a() }); }`
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What's the point of !function? Just to draw attention that it's not being used?

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@maxmilton maxmilton Aug 31, 2018 •
edited
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It turns it from a function declaration into an expression, see: https://stackoverflow.com/questions/3755606/what-does-the-exclamation-mark-do-before-the-function

As for why I'm not entirely sure.

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The input is a function expression, too.

},

{
description: 'transpiles await function call',
input: `async function f() { await a(); }`,
output: `function f() { return Promise.resolve().then(function() { return a(); }).then(function() {}) }`
},

{
description: 'transpiles await function call with return statement',
input: `async function f() { return await a(); }`,
output: `function f() { return Promise.resolve().then(function() { return a(); }) }`
},

{
description: 'transpiles await function call with more than one line of code',
input: `async function f() { await a(); thing(); await a2(); stuff(); await a3(); await a4(); }`,
output: `function f() { return Promise.resolve().then(function() { return a(); }) .then(function() { thing(); }) .then(function() { return a2(); }) .then(function() { stuff(); }) .then(function() { return a3(); }) .then(function() { return a4(); }).then(function() {}) }`
}
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there is not test that verifies return values and closures

	{
		description: 'transpiles await function call with normal return statement',
		input: `async function f() { var x = 1; await a(); return x; }`,
        output: `...`
	},

];