ES7:
const a = function(val) {
return new Promise(function(resolve, reject) {
if (val > 5) {
resolve(val * val);
} else {
reject(val);
}
});
};
const b = async function () {
const val = await a(6);
console.log(val);
};
b();
转成ES5,可见底层是用promise来实现的:
function _asyncToGenerator(fn) { return function () { var gen = fn.apply(this, arguments); return new Promise(function (resolve, reject) { function step(key, arg) { try { var info = gen[key](arg); var value = info.value; } catch (error) { reject(error); return; } if (info.done) { resolve(value); } else { return Promise.resolve(value).then(function (value) { return step("next", value); }, function (err) { return step("throw", err); }); } } return step("next"); }); }; }
const a = function (val) {
return new Promise(function (resolve, reject) {
if (val > 5) {
resolve(val * val);
} else {
reject(val);
}
});
};
const b = (() => {
var ref = _asyncToGenerator(function* () {
const val = yield a(6);
console.log(val);
});
return function b() {
return ref.apply(this, arguments);
};
})();
b();