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AJAX: Check if a string is JSON?

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甜味超标
甜味超标 2020-12-02 21:32

My JavaScript sometimes crashes on this line:

var json = eval(\'(\' + this.responseText + \')\');

Crashes are caused when the argument of <

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7条回答
  • 花落未央
    2020-12-02 22:13

    There is a tiny library that checks JavaScript types: is.js

    is.json({foo: 'bar'});
=> true

// functions are returning as false
is.json(toString);
=> false

is.not.json([]);
=> true

is.all.json({}, 1);
=> false

is.any.json({}, 2);
=> true

// 'all' and 'any' interfaces can also take array parameter
is.all.json([{}, {foo: 'bar'}]);
=> true

    Actually is.js is much more then this, some honorable mentions:

    var obj = document.createElement('div');
is.domNode(obj);
=> true

is.error(new Error());
=> true

is.function(toString);
=> true

is.chrome();
=> true if current browser is chrome
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  • 暗喜
    2020-12-02 22:18

    The problem with depending on the try-catch approach is that JSON.parse('123') = 123 and it will not throw an exception. Therefore, In addition to the try-catch, we need to check the type as follows:

    function isJsonStr(str) {
    var parsedStr = str;
    try {
        parsedStr = JSON.parse(str);
    } catch (e) {
        return false;
    }
    return typeof parsedStr == 'object'
}
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  • 遇见更好的自我
    2020-12-02 22:20

    Maybe this helps: With this code, you can get directly your data…

    <!DOCTYPE html>
<html>
<body>

<h3>Open console, please, to view result!</h3>
<p id="demo"></p>

<script>
var tryJSON = function (test) {
	try {
	    JSON.parse(test);
	}
	catch(err) {
    	// maybe you need to escape this… (or not)
	    test = '"'+test.replace(/\\?"/g,'\\"')+'"';
	}
	eval('test = '+test);
	console.debug('Try json:', test);
};

// test with string…
var test = 'bonjour "mister"';
tryJSON(test);
// test with JSON…
var test = '{"fr-FR": "<p>Ceci est un texte en français !</p>","en-GB": "<p>And here, a text in english!</p>","nl-NL": "","es-ES": ""}';
tryJSON(test);
</script>

</body>
</html>

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  • 谎友^
    2020-12-02 22:20

    Why you can't just check what is the response? It is more more efficient.

    var result;

if (response.headers['Content-Type'] === 'application/json')
    result = JSON.parse(this.responseText);
else
    result = this.responseText;

    screen1

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  • 栀梦
    2020-12-02 22:23

    I highly recommend you use a javascript JSON library for serializing to and from JSON. eval() is a security risk which should never be used unless you are absolutely certain that its input is sanitized and safe.

    With a JSON library in place, just wrap the call to its parse() equivalent in a try/catch-block to handle non-JSON input:

    try
{
  var jsonObject = JSON.parse(yourJsonString);
}
catch(e)
{
  // handle error 
}
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  • 渐次进展
    2020-12-02 22:29

    If you include the JSON parser from json.org, you can use its parse() function and just wrap it in a try/catch, like so:

    try
{
   var json = JSON.parse(this.responseText);
}
catch(e)
{
   alert('invalid json');
}

    Something like that would probably do what you want.

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