How can I pretty-print JSON in JavaScript and add syntax highlighting?

Pretty-Printing JSON in JavaScript

Displaying JSON in a human-readable format is essential for comprehending and debugging data. In JavaScript, this is achieved through the native JSON.stringify() function.

Native Pretty-Printing:

The third argument of JSON.stringify() enables pretty-printing and specifies the indentation level. For instance:

var str = JSON.stringify(obj, null, 2); // spacing level = 2

This will output JSON with 2 spaces of indentation, making it easier to read.

Syntax Highlighting:

For more elaborate formatting, you can use regular expressions to highlight different elements within the JSON string.

function syntaxHighlight(json) {
  return json.replace(/("(\u[a-zA-Z0-9]{4}|\[^u]|[^\"])*"(\s*:)?|\b(true|false|null)\b|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?)/g, function (match) {
    var cls = 'number';
    if (/^"/.test(match)) {
      if (/:$/.test(match)) {
        cls = 'key';
      } else {
        cls = 'string';
      }
    } else if (/true|false/.test(match)) {
      cls = 'boolean';
    } else if (/null/.test(match)) {
      cls = 'null';
    }
    return '<span class="' + cls + '">' + match + '</span>';
  });
}

This function replaces certain patterns with HTML tags to apply styles such as color to different JSON elements.

Full Code Snippet:

Here's a comprehensive example:

function output(inp) {
  document.body.appendChild(document.createElement('pre')).innerHTML = inp;
}

function syntaxHighlight(json) {
  return json.replace(/&amp;/g, '&amp;amp;').replace(/</g, '&amp;lt;').replace(/>/g, '&amp;gt;');
}

var obj = {a:1, 'b':'foo', c:[false,'false',null, 'null', {d:{e:1.3e5,f:'1.3e5'}}]};
var str = JSON.stringify(obj, undefined, 4);

output(str);
output(syntaxHighlight(str));

This script parses a JSON object, pretty-prints it, and displays it along with syntax-highlighted JSON.

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