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Cover image for Show JSON As Pretty Print With Syntax Highlighting in React
Gaurav Adhikari
Gaurav Adhikari

Posted on • Updated on

Show JSON As Pretty Print With Syntax Highlighting in React

#javascript #react #css #html

In this post, we will learn how to show the JSON data as pretty printed, and with colored highlighted syntax in our ReactJS/JS apps.

Coming straight to the utility function below

export function syntaxHighlight(json) {
  if (!json) return ""; //no JSON from response

  json = json
    .replace(/&/g, "&")
    .replace(/</g, "&lt;")
    .replace(/>/g, "&gt;");
  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>";
    }
  );
}
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and the CSS

pre {
  outline: 1px solid #ccc;
  padding: 5px;
  margin: 15px;
}
.string {
  color: green;
}
.number {
  color: darkorange;
}
.boolean {
  color: blue;
}
.null {
  color: magenta;
}
.key {
  color: red;
}
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Now we can use our syntaxHighlight function, just pass it with JSON to prettify and highlight

Example usage in ReactJS app:

import { useEffect, useState } from "react";

import { syntaxHighlight } from "./utils";
import "./styles.css";

export default function App() {
  const [ourJSON, setOurJSON] = useState();

  useEffect(() => {
    fetch("https://jsonplaceholder.typicode.com/todos/1")
      .then((response) => response.json())
      .then((json) => setOurJSON(json));
  }, []);

  return (
    <div>
      <h3 className="header">
        Show JSON As Pretty Print With Syntax Highlighting
      </h3>
      <pre
        dangerouslySetInnerHTML={{
          __html: syntaxHighlight(JSON.stringify(ourJSON, undefined, 4))
        }}
      />
    </div>
  );
}
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Credit for utility function

Happy Coding, Thanks!

Top comments (3)

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katheesh profile image
кαтнєєѕкυмαɾ •

simply & nice

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gauravadhikari1997 profile image
Gaurav Adhikari •

I am glad you like it!

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zedemian profile image
Demian Blacksmith • • Edited

just more minified the same css+js, but with ability JSON stringify input argument:

.string {color: green} .number {color: darkorange} .boolean {color: blue} .null {color: magenta} .key {color: red}
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const highlight = json => (!(json = typeof json !== "string" ? JSON.stringify(json, null, 2) : json)) ? ""
        : json.replace(/&/g, "&amp;").replace(/</g, "&lt;").replace(/>/g, "&gt;").replace(
            /("(\\u[a-zA-Z0-9]{4}|\\[^u]|[^\\"])*"(\s*:)?|\b(true|false|null)\b|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?)/g,
            val => '<span class="'+(/^"/.test(val) ? (/:$/.test(val)?"key":"string")
                : (/true|false/.test(val) ? "boolean" : (/null/.test(val)?"null":"number")))+'">'+val+"</span>"
        );
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