How decode HEX in XMLHtppRequest?

Question

I have a site and I used AJAX. And I got some problems.

Server return JSON string something like this {a:"x48\\x65\\x6C\\x6C\\x6F"} .

Then in xx.responseText , we have this string '{a:"\\x48\\x65\\x6C\\x6C\\x6F"}' .

But if I create JavaScript string "\\x48\\x65\\x6C\\x6C\\x6F" then I have "Hello" and not HEX!

Is it possible get in xx.responseText "real" text from HEX (automatically, without .replace() )?

Answer 1

If the output is at all regular (predictable), .replace() is probably the simplest.

var escapeSequences = xx.responseText.replace(/^\{a:/, '').replace(/\}$/, '');

console.log(escapeSequences === "\"\\x48\\x65\\x6C\\x6C\\x6F\""); // true

Or, if a string literal that's equivalent in value but may not otherwise be the same is sufficient, you could parse (see below) and then stringify() an individual property.

console.log(JSON.stringify(data.a) === "\"Hello\""); // true

Otherwise, you'll likely need to run responseText through a lexer to tokenize it and retrieve the literal from that. JavaScript doesn't include an option for this separate from parsing/evaluating, so you'll need to find a library for this.

" Lexer written in JavaScript? " may be a good place to start for that.

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To parse it:

Since it appears to be a string of code, you'll likely have to use eval() .

var data = eval('(' + xx.responseText + ')');

console.log(data.a); // Hello

Note: The parenthesis make sure {...} is evaluated as an Object literal rather than as a block .

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Also, I'd suggest looking into alternatives to code for communicating data like this.

A common option is JSON , which takes its syntax from JavaScript, but uses a rather strict subset. It doesn't allow function s or other potentially problematic code to be included.

var data = JSON.parse(xx.responseText);

console.log(data.a); // Hello

Visiting JSON.org , you should be able to find a reference or library for the choice of server-side language to output JSON.

{ "a": "Hello" }

Answer 2

Why not just let the JSON parser do its job and handle the \\x escape sequences, and then just convert the string back to hex again afterwards, eg

function charToHex(c) {
    var hex = c.charCodeAt(0).toString(16);
    return (hex.length === 2) ? hex : '0' + hex;
}

"Hello".replace(/./g, charToHex);  // gives "48656c6c6f"