Simple utility to print difference between JSON files

diff_json.js

/* Print out differences between two JSON files
*/
'use strict'

const _ = require('lodash');
const path = require('path');


/**
 * Print out all differences between two objects
 * @param a - First object
 * @param b - Second object
 * @param a_name - Name of first object
 * @param b_name - Name of second object
 * @param prefix - Used during recursive calls to keep track of subobject keys.
 */
function diff(a, b, a_name, b_name, prefix='') {
    // If prefix is nonempty, it is a key and needs a
    const pref = (prefix == '')
        ? prefix
        : `${prefix}.`
    const a_keys = new Set(_.keys(a));
    const b_keys = new Set(_.keys(b));

    const not_in_b = [...a_keys].filter(x => !b_keys.has(x));
    if(not_in_b.length > 0)
        console.log(`Keys not in ${b_name}: ${_.map(not_in_b, (key) => pref + key.toString())}`);

    const not_in_a = [...b_keys].filter(x => !a_keys.has(x));
    if(not_in_a.length > 0)
        console.log(`Keys not in ${a_name}: ${_.map(not_in_a, (key) => pref + key.toString())}`);

    const keys_in_both = [...a_keys].filter(x => b_keys.has(x));
    keys_in_both.forEach((key) => {
        // Deep equality check
        if(!_.isEqual(a[key], b[key])) {
            // Recursively check subobjects for differences
            if(a[key] instanceof Object || b[key] instanceof Object) {
                diff(a[key], b[key], a_name, b_name, `${pref}${key}`);
            }
            else {
                // Case where one value is int and another is string
                if(a[key].toString() == b[key].toString())
                    console.log(`${pref}${key}: ${a_name}==${a[key]} is type ${typeof(a[key])}, but  ${b_name}==${b[key]} is type ${typeof(b[key])}`);
                else
                    console.log(`${pref}${key}: ${a_name}==${a[key]} != ${b_name}==${b[key]}`);
            }
        }

    });
}

if(process.argv.length < 4) {
    throw Error("You must provide 2 JSON files to diff");
}

const file1 = process.argv[2];
const file2 = process.argv[3];

let a = undefined
try {
    a = require(file1);
}
catch (e) {
    console.log(`Unable to load JSON from file ${file1}`);
    throw e;
}
let b = undefined
try {
    b = require(file2);
}
catch (e) {
    console.log(`Unable to load JSON from file ${file2}`);
    throw e
}

const a_name = path.basename(file1).replace('.json', '');
const b_name = path.basename(file2).replace('.json', '');

console.log('');
diff(a, b, a_name, b_name);