js0023

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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>