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C# 6.0 has just been released and has a new nice little feature that I'd really like to use in JavaScript. They're called Null-conditional operators. These use a ?. or ?[] syntax.
What these do is essentially allow you to check that the object you've got isn't null, before trying to access a property. If the object is null, then you'll get null as the result of your property access instead.
int? length = customers?.Length; So here int can be null, and will take that value if customers is null. What is even better is that you can chain these:
int? length = customers?.orders?.Length; I don't believe we can do this in JavaScript, but I'm wondering what's the neatest way of doing something similar. Generally I find chaining if blocks difficult to read:
var length = null; if(customers && customers.orders) { length = customers.orders.length; } 
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Null-conditional operators ?. and ?[] Available in C# 6 and later, a null-conditional operator applies a member access, ?. , or element access, ?[] , operation to its operand only if that operand evaluates to non-null; otherwise, it returns null .
Introduced in C# 6.0, the Null Conditional Operator ?. will immediately return null if the expression on its left-hand side evaluates to null , instead of throwing a NullReferenceException . If its left-hand side evaluates to a non- null value, it is treated just like a normal .
The ?? operator is used to check null values and you can also assign a default value to a variable whose value is null(or nullable type).
In cases where a statement could return null, the null-coalescing operator can be used to ensure a reasonable value gets returned. This code returns the name of an item or the default name if the item is null. As you can see, this operator is a handy tool when working with the null-conditional operator.
Called "optional chaining", it's currently a TC39 proposal in Stage 4. A Babel plugin however is already available in v7.
Example usage:
const obj = { foo: { bar: { baz: 42, }, }, }; const baz = obj?.foo?.bar?.baz; // 42 const safe = obj?.qux?.baz; // undefined Js logical operators return not true or false, but truly or falsy value itself. For example in expression x && y, if x is falsy, then it will be returned, otherwise y will be returned. So the truth table for operator is correct.
In your case you could use expression customers && customers.orders && customers.orders.Length to get length value or the first falsy one.
Also you can do some magic like ((customers || {}).orders || {}).length (Personally, I don't like this syntax and possible garbage collection pressure as well)
Or even use maybe monad.
function Option(value) { this.value = value; this.hasValue = !!value; } Option.prototype.map = function(s) { return this.hasValue ? new Option(this.value[s]) : this; } Option.prototype.valueOrNull = function() { return this.hasValue ? this.value : null; } var length = new Option(customers) .map("orders") .map("length") .valueOrNull(); It's longer than all the previous approaches, but clearly shows your intentions without any magic behind.
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