Uncertain behaviour of _.get-CodePudding

let a = {
   b  : null
}

_.get(a, 'b',''); //return null

but

_.get (a, null, '') //return ''

Is null a falsy value for _.get()?

let a = {
   b  : {c:{
}
} //basically a nested object

I'm trying to do _.get(a, 'b.c','').toString() and I'm getting error because _.get return null. What is the best readable way to write this?

CodePudding user response：

The third argument defaultValue will only be returned for undefined resolved values, not null. see docs

If you want a fallback value for null or undefined, use the nullish coalescing operator:

(_.get(a, "b.c") ?? "").toString()

Below are different results using different mechanisms in defining default value:

let a;

a = { b: null };
_.get(a, "b", ""); // null
_.get(a, "b") ?? ""; // ""
_.get(a, "b") || ""; // ""

a = { };
_.get(a, "b", ""); // ""

a = { b: undefined };
_.get(a, "b", ""); // ""

a = { b: 0 };
_.get(a, "b") || ""; // ""
_.get(a, "b") ?? ""; // 0

CodePudding user response：

_.get(a, 'b','');

you ask for the property a['b'], which happens to be null, which isn't undefined, so you get null as the final result. Next, in

_.get(a, null, '');

you ask for the property a['null'], which doesn't exist, so it's undefined, and you end up with the fallback value ''. Finally, with

let a = {b: {c: {}}};
_.get(a, 'b.c', '');

you seem to be asking for a['b']['c'], which would be an empty object. However, the dotted path notation is Lodash-specific. If you are using Underscore, the path is interpreted as a['b.c'] by default, which doesn't exist and is undefined. In that case, you should get '' as the final result. I see no way this expression could result in null, even if you are using the original value of a = {b: null}.

If you are, in fact, using Underscore and you want to retrieve the nested c object within the b property, you have two options. Firstly, you can use array path notation, which is portable between Underscore and Lodash:

_.get(a, ['b', 'c'], '');

Secondly, you can override _.toPath to enable dotted path notation for all Underscore functions:

const originalToPath = _.toPath;
_.toPath = function(path) {
    if (_.isString(path)) return path.split('.');
    return originalToPath(path);
}

_.get(a, 'b.c', '');

I wouldn't recommend this, because it can break code that is trying to retrieve properties that contain the period character . in the name. I mention it for completeness; use your own judgment.