JavaScript: Assigns default values for all properties in an object that are undefined

JavaScript fundamental (ES6 Syntax): Exercise-247 with Solution

Assign Defaults to Object

Write a JavaScript program that assigns default values to all undefined properties in an object.

• Use Object.assign() to create a new empty object and copy the original one to maintain key order.
• Use Array.prototype.reverse() and the spread operator (...) to combine the default values from left to right.
• Finally, use obj again to overwrite properties that originally had a value.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2 
// Define a function 'defaults' to merge multiple objects with the same keys, prioritizing the values from right to left
const defaults = (obj, ...defs) => Object.assign({}, obj, ...defs.reverse(), obj);

// Call the 'defaults' function with an object and multiple default objects, and log the merged result
console.log(defaults({ a: 1 }, { b: 2 }, { b: 6 }, { a: 3 }));

Output:

{"a":1,"b":2}

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-247-1 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript program that assigns default values to undefined properties in an object without mutating the original.
• Write a JavaScript function that merges a default settings object with a user-specified object.
• Write a JavaScript program that iterates over an object and assigns a fallback value for any missing keys.
• Write a JavaScript function that returns a new object with defaults filled in for any undefined properties.

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