Prepack——让JavaScript代码运行更快速

1
2
3
4
5
6
优化前：
(function () {
  function hello() { return 'hello'; }
  function world() { return 'world'; }
  global.s = hello() + ' ' + world();
})();

1
2
3
4
优化后：
(function () {
  s = "hello world";
})();

1
2
3
4
5
6
7
8
9
 优化前：
(function () {
  var self = this;
  ['A', 'B', 42].forEach(function(x) {
    var name = '_' + x.toString()[0].toLowerCase();
    var y = parseInt(x);
    self[name] = y ? y : x;
  });
})();

1
2
3
4
5
6
优化后：
(function () {
  _a = "A";
  _b = "B";
  _4 = 42;
})();

1
2
3
4
5
6
7
优化前：
(function () {
  function fibonacci(x) {
    return x <= 1 ? x : fibonacci(x - 1) + fibonacci(x - 2);
  }
  global.x = fibonacci(23);
})();

1
2
3
4
优化后：
(function () {
  x = 28657;
})();

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
优化前：
(function () {
  let moduleTable = {};
  function define(id, f) { moduleTable[id] = f; }
  function require(id) {
    let x = moduleTable[id];
    return x instanceof Function ? (moduleTable[id] = x()) : x;
  }
  global.require = require;
  define("one", function() { return 1; });
  define("two", function() { return require("one") + require("one"); });
  define("three", function() { return require("two") + require("one"); });
  define("four", function() { return require("three") + require("one"); });
})();
three = require("three");

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
优化后：
(function () {
  function _2() {
    return 3 + 1;
  }

  var _1 = {
    one: 1,
    two: 2,
    three: 3,
    four: _2
  };

  function _0(id) {
    let x = _1[id];
    return x instanceof Function ? _1[id] = x() : x;
  }

  require = _0;
  three = 3;
})();

1
2
3
4
5
6
7
 优化前：
(function(){
  function fib(x) { return x <= 1 ? x : fib(x - 1) + fib(x - 2); }
  let x = Date.now();
  if (x === 0) x = fib(10);
  global.result = x;
})();

1
2
3
4
5
6
7
8
优化后：
(function () {
  var _0 = Date.now();
  if (typeof _0 !== "number") {
    throw new Error("Prepack model invariant violation");
  }
  result = _0 === 0 ? 55 : _0;
})();

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
// Assume that a certain property has a simple known value.
__assumeDataProperty(global, "obscure", undefined);
// Assume that a certain property has a simple unknown value.
__assumeDataProperty(global, "notSoObscure", __abstract());
// Assume that a richly structured value exists
__assumeDataProperty(global, "rich", __abstract({
  x: __abstract("number"),
  y: __abstract("boolean"),
  z: __abstract("string"),
  nested: __abstract({
    x: __abstract()
  })
}));
// Forbid any accesses to an object except at known positions
__makePartial(global);
// At this point, accessing global.obscure, global.notSoObscure, global.rich.nested.x is okay,
// but accessing global.unknown or global.rich.unknown would cause an introspection error.

// The following tells Prepack to embed and call some code in the residual program.
// The code must not have any side effects on the reachable JavaScript heap.
__residual("object", function(delay) {
  return global.pushSelfDestructButton(delay);
}, "5 minutes");