JavaScript: Compare two objects to determine if the first one contains equivalent property values to the second one, based on a provided function

JavaScript fundamental (ES6 Syntax): Exercise-179 with Solution

Object Comparison by Function

Write a JavaScript program to compare two objects to determine if the first contains equivalent property values to the second one. This is based on a provided function.

• Use Object.keys() to get all the keys of the second object.
• Use Array.prototype.every(), Object.prototype.hasOwnProperty() and the provided function to determine if all keys exist in the first object and have equivalent values.
• If no function is provided, the values will be compared using the equality operator.

Sample Solution:

JavaScript Code:

// Define a function 'matchesWith' that takes three arguments: 'obj', 'source', and 'fn'
const matchesWith = (obj, source, fn) =>
  // Check if every key in 'source' satisfies a condition
  Object.keys(source).every(
    // Callback function for 'every' with parameters 'key' representing the current key
    key =>
      // Check if 'obj' has the key 'key' and whether 'fn' exists
      obj.hasOwnProperty(key) && fn
        // If both conditions are true, call the function 'fn' with parameters
        ? fn(obj[key], source[key], key, obj, source)
        // If 'fn' doesn't exist, compare the values of 'obj[key]' and 'source[key]'
        : obj[key] == source[key] // If they are equal, return true; otherwise, return false
  );

// Define a function 'isGreeting' that checks if a string is a greeting ('hi' or 'hello')
const isGreeting = val => /^h(?:i|ello)$/.test(val);

// Call 'matchesWith' with two objects and a custom comparison function
console.log(matchesWith(
  { greeting: 'hello' }, // Object 'obj' with property 'greeting' set to 'hello'
  { greeting: 'hi' }, // Object 'source' with property 'greeting' set to 'hi'
  // Custom comparison function to check if both values are greetings using 'isGreeting' function
  (oV, sV) => isGreeting(oV) && isGreeting(sV)
));

Output:

true

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-179-1 by w3resource (@w3resource) on CodePen.

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