function filterArray(array, callback) {
const newArray = [];
for (let i = 0; i < array.length; i += 1) {
if (callback(array[i])) newArray.push(array[i]);
}
return newArray;
}
I'm confused by the syntax. Typically what I've seen so far is
if (condition) {
// code to be executed
}
where condition is some boolean statement which will run the code shown if condition = true.
But, in this if statement, there is no boolean, nor is there code to be executed after the conditonal statement. I have no clue what it means. Thanks in advance for any help interpeting it.
(callback(array[i])) this part is the condition. newArray.push(array[i]) this is what happens when the condition is met. It just looks so close together.
if (callback(array[i]))
{
newArray.push(array[i])
}Does same thing.
There is a boolean, namely the value returned from calling the function callback with argument array[i]. (To be precise: The interpretation of the returned value as a truth value according to the JavaScript language specs - this is what is meant by 'truthy' or 'falsy'. For starters just assume that callback does indeed return a boolean value)
There also is code being executed: The first statement after the condition. This is just a notational shorthand. The verbose equivalent code would be:
if (callback(array[i])) {
newArray.push(array[i]);
}
if (callback(array[i])) newArray.push(array[i]); simply means that callback is a function, that gets called and a return value is expected (could be any value, not only boolean). Then, if the return is truthy, the statement newArray.push(array[i]); gets executed.
(A single line if (exp) statement; can be written like this, but may sometimes hide bugs, so some linters prefer to always change it to
if (exp) {
statement;
}
Callbacks are typically functions that get passed in as an argument (exactly as you see here) that then may get called.