Get

Get

Question

Before the optional chaining operator (?.) existed, it was sometimes troublesome to access deeply-nested properties in huge JavaScript objects when some of the intermediate properties might not be present.const john = { profile: { name: { firstName: 'John', lastName: 'Doe' }, age: 20, gender: 'Male', },};const jane = { profile: { age: 19, gender: 'Female', },};function getFirstName(user) { return user.profile.name.firstName;}Doing getFirstName(john) works but getFirstName(jane) will error because the name property doesn't exist for jane.profile.

Lodash's Get method

Lodash's _.get method was created as a solution for such use cases.Let's write our own version as a get function. The function gets the value at path of object. If the resolved value is undefined, the defaultValue is returned in its place. The function signature is as such:get(object, path, [defaultValue]);

• object: The object to query.

• path: The path of the property to get. It can be a string with . as the separator between fields, or an array of path strings.

• defaultValue: Optional parameter. The value returned if the resolved value is undefined.

Examples

get(john, 'profile.name.firstName'); // 'John'get(john, 'profile.gender'); // 'Male'get(jane, 'profile.name.firstName'); // undefinedArrays can also be accessed if numerical indices are provided.get({ a: [{ b: { c: 3 } }] }, 'a.0.b.c'); // 3There's no need to support syntax resembling get(object, 'a[0].b.c').​

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AnswerThe tricky part of the question is to see that some form of iteration/recursion has to be done on the object to access nested fields.

Solution

The first step is to split up the path by the delimiter, which is a period. Then we have to recursively traverse the object given each token in the path, which can be done either with while/for loops or recursions. The looping should stop when a null-ish value is encountered.Array index accessing doesn't require special handling and can be treated like accessing string-based fields on objects.