Can someone help me interpret the if statement in this javascript code?-CodePudding

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.

CodePudding user response：

(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.

CodePudding user response：

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]);
}

CodePudding user response：

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.

CodePudding user response：

If your condition isn't working try to use a if else loop. If your statement isn't what you expect show an error message, else push array[i];

function filterArray(array, callback) {
  const newArray = [];
  for (let i = 0; i < array.length; i  = 1) {
    if (!callback(array[i])){
       console.log('Something went wrong');
  }else{
       newArray.push(array[i]);
    }
  return newArray;
}
´´´

Since you only give this piece of code, it's hard to analyze it, but this may work