js0023

创建真实的promise 案例

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<!DOCTYPE html>
<html>
<head>
<title>Creating a JSON promise</title>
<meta charset="utf-8">
<link rel="stylesheet" href="../assert.css">
<script src="../assert.js"></script>
<script>
function getJSON(url) {
return new Promise((resolve, reject) => {
const request = new XMLHttpRequest();
request.open("GET", url);

request.onload = function() {
try {
if(this.status === 200 ){
resolve(JSON.parse(this.response));
} else{
reject(this.status + " " + this.statusText);
}
} catch(e){
reject(e.message);
}
};

request.onerror = function() {
reject(this.status + " " + this.statusText);
};

request.send();
});
}

getJSON("data/ninjas.json").then((ninjas) => {
assert(ninjas !== null, "Ninjas obtained!");
}).catch(e => fail("Shouldn’t be here:" + e));
</script>
</head>
<body>
<p>Has to be executed on a server (e.g MAMP, WAMP)</p>
</body>
</html>