Why can if statement works using an object (like Map) with “.has()” and no working with “.includes”?

That’s my code to explain my idea better (I’m a non english speaker):

The “.includes()” method doesn’t work in this case

const sentence = "hello world hello boy";

let words = sentence.split(" ");

const quantWords = new Map();

for (let word of words) {  
    if (quantWords.includes(word)) {
        quantWords.set(word, + 1);
    } else {
        quantWords.set(word, 1);
    }
}
console.log(quantWords);

Otherwise, using “.has()”, it works

const sentence = "hello world hello boy";

let words = sentence.split(" ");

const quantWords = new Map();

for (let word of words) {  
    if (quantWords.has(word)) {
        quantWords.set(word, + 1);
    } else {
        quantWords.set(word, 1);
    }
}
console.log(quantWords);