Consider I have a object like this:
Obj.Boo.Foo.Zoo
Ok now if I want to be sure that zoo has a value and not empty, I should do:
if(Obj != null && Obj.Boo != null && Obj.Boo.Foo != null && Obj.Boo.Foo.Zoo != null) {
//blah blah
}
And If I have more nested objects after Zoo, I should expand the if and the code becomes a little bit malformed.
Is there any better way for doing that type of conditions?
I keep a little function I call chainGet(obj, chain, default) around for situations just like this:
function chainGet(obj, chain, dflt) {
if (typeof chain === "string")
chain = chain.split(".");
var result = obj;
for (var i = 0; i < chain.length; i += 1) {
if (result === undefined)
break;
result = result[chain[i]];
}
return result === undefined? dflt : result;
}
For example:
> chainGet({ foo: 42 }, "foo")
42
> chainGet({ foo: 42 }, "bar", "x")
'x'
> chainGet({ foo: { bar: 42 }}), "foo.bar")
42
This even works with arrays:
> chainGet([{ foo: [42] }], [0, "foo", 0])
42
Of course, long chains of dotted accesses are a code smell, so caution should be exercised when using them… but sometimes you've just got to do it ;)
default, and result is changed to obj[chain[i]], which means its never going deeper into the object. I tried to change the code, David, but it looks like you declined it.
default? Isn't that a reserved keyword? You should rename default to something else.A bad practice if you dont really need to handle such a case would be to try accessing the Object in a try catch statement
try{
// access Obj.Boo.Foo.Zoo
}
catch{
// catch a NullReferenceException
}
A better way would be to modify your getters and setters so that the parent object throws a suitable exception or handles this once you try to access a subobject and its null. In this case it would be enough to check the first object.
try { var x = foo.bar.baz; } catch(e) { … }; x(); -- making sure to use the value outside of the try block, so the only exception that will be caught is the npx from the chain lookup.
It can be achieved without using a function. Shortcut method could be -
if(((((Obj || {}).Boo || {}).Foo || {}).Zoo || {}) != {}) {
// Zoo has a value and not empty
}
Or the ES6 way -
const checkNull = (keys, Object) =>
keys.reduce((Obj, o) =>
(Obj && Obj[o]) ? Obj[o] : null, Object)
console.log(checkNull(['Boo', 'Foo', Zoo], Obj))
// [Value of Zoo]
console.log(checkNull(['Boo', 'Foo1', Zoo], Obj))
// null
