I am writing a program to concatenate a string to make it repeat a number of times but on using concat method it always returns an empty string. I have solved the problem using + operator. But I still want to figure why concat is returning empty string.
Here is the code
let repeatStr = (str, num) => {
let newStr = '';
for(let i = 0; i < num; i++){
newStr.concat(str);
}
return newStr;
}
I believe it is because concat method does not modify the string in-place, and you need to assign its result to some variable. If instead you replace that line in your code with newStr = newStr.concat(str); it should work fine.
This is because .concat() returns a new string, and the original is unmodified. You can reassign to the same variable.
Note: You can also use the + operator.
let repeatStr = (str, num) => {
let newStr = '';
for(let i = 0; i < num; i++){
//newStr = newStr.concat(str); //Both work
newStr += str;
}
return newStr;
}
console.log(repeatStr('x',3));
concat returns with string not array
concat is method on both the string and array prototype. And it returns the new value in both the cases.string not arrayIf you check the definition of concat in MDN
The
concat()method concatenates the string arguments to the calling string and returns a new string.
that is means that it doesn't change the old value of your variable so all you need is to re-assign your variable with the new value
let repeatStr = (str, num) => {
let newStr = '';
for(let i = 0; i < num; i++){
newStr = newStr.concat(str);
}
return newStr;
}
console.log(repeatStr('welcome', 2))there is another simple solution you could use repeat function it used for this purpose like this
console.log("welcome".repeat(3))
String.prototype.repeatfunction to repeat a string rather than creating a new function