I have this code in typescript:
console.log ('collection[0] -> ' + collection[0] );
console.log ('collection[0] !== null -> ' + collection[0] !== null);
but this is the result on the console:
console.log src/services/service.ts:122
collection[0] -> null
console.log src/services/service.ts:123
true
I bet your collection[0] is a string containing 'null', not the primitive value null. Try:
console.log (collection[0] !== 'null');
It could also be an object that results in 'null' when cast to string:
const item = collection[0];
const isWeirdNullObj = typeof item === 'object' && item !== null && String(item) === 'null';
This could happen with something like the following:
const item = {
valueOf() {
return 'null';
}
};
console.log('item is ' + item);
console.log(typeof item);
typeof collection[0]'null' when cast to string. Pretty weirdAddition operator has precedence over the equality operator.
So, in your code the addition operation is being evaluated first. Try the following :-
console.log ('collection[0] !== null -> ' + (collection[0] !== null));
You have been burned by JavaScript's type coercion. The + operator in JS has a lot of operations associated with it. I suggest you don't concat with it and string interpolate instead.
console.log(`collection[0] !== null -> ${collection[0] !== null}`);
Your other option is to separate out the two operations with a comma. console.log can take an arbitrary number of arguments and combines them for you
console.log ('collection[0] !== null -> ', collection[0] !== null);
Use , instead of + if you want to log some variable:
var collection = [null];
console.log ('collection[0] -> ', collection[0] );
console.log ('collection[0] !== null -> ', collection[0] !== null);