如何正确警告数组/ for循环中的项目？

Question

I am doing a project with converting a simple sentence to a statement that an 'adolescent' would say. I want to add the phrase 'you know' after each three words in the sentence that the user types in. When I print the converted sentence at the end, it seems as though there is an extra 'you know' for each one of my items (or words) in my array. How do I lose all of the extra 'you know''s at the end? Or how do I prevent that from happening? Here is my code:

var k = 3;
var phrase = "you know";
var sentence = prompt("Enter a sentence: ");
sentence = sentence.split(" ");

for (word in sentence) {
  sentence.splice(k, 0, phrase);
  k += 4;
}

sentence = sentence.join(" ");

alert(sentence);

Answer 1

for of vs for in

When you want to iterate over every item in an iterable (such as an array), you should use for (let x of arr) ... instead of for (let x in arr) . The latter is used for iterating over every key in an object, including prototypically inherited ones.

Mutating what you iterate

You are iterating over a thing and modifying it at the same time, which is always a good recipe for a headache. If you are going to mutate an array incrementally while traversing it, make a copy first: var newSentence = sentence.slice() , then modify that. In fact, you don't even really need to iterate the array because...

Too many "you knows"

Your logic is a little bit off. For an N-word sentence, you inject "you know" exactly N times; which only makes sense if you want one "you know" per word. If you want to insert every 4 words, you need to insert N / 4 times. What you need is to simply keep inserting while you haven't run off past the end of the sentence:

var k = 3;
var phrase = "you know";
var sentence = prompt("Enter a sentence: ");
sentence = sentence.split(" ");

while (k <= sentence.length) {
  sentence.splice(k, 0, phrase);
  k += 4;
}

sentence = sentence.join(" ");

alert(sentence);

Answer 2

See the for loop below, which starts after the third word and increments by three words (plus the phrase we just inserted) with each iteration, stopping at the end of the sentence:

 var phrase = "you know"; var sentence = "This is a sentence with a bunch of words in it."; // test data instead of prompt var words = sentence.split(" "); for (var i = 3; i <= words.length; i += 4) { words.splice(i, 0, phrase); } console.log(words.join(" ")); // instead of alert 

The issue with your code is that your loop executes n times, where n is the number of words in the sentence. You could fix your loop by break ing when k goes off the end of the sentence, but it's simpler to just construct a better for loop.

Answer 3

Here you go

var sentence = prompt("Enter a sentence: ");
sentence = sentence.split(" ");
var newSentence = [];
for(var i = 0;i<sentence.length;i++){
 if(i!=0 && i%3==0 && i<(sentence.length-1)){
  newSentence.push("you know");
 }
newSentence.push(sentence[i]);
}
sentence = newSentence.join(" ");