Why it is print undefined? not length of the word

 var str=prompt("Enter the string;").split(" ");
       var lent=str.map(function(x){
           return {
               x : x.length
       document.write("<br>The length is 1 word is :"+lent[0][str[0]]);

So say you have a string `“Hello I am a string”, your map produces an array like:

[{ x: 5}, {x: 1}, {x: 2}, {x: 1}, {x: 6}]

You then pick the first item (lent[0]), and then try to access a sub-index that doesn’t exist ([str[0]]).

then how to access the value of the key…please tell me.

For some reason you’ve created an object: {x: length} where length is the length of the word. You just access it like any other object, it has a key that you’ve called x. Like lent[0] is {x: 5} in my example, it’s literally that.

lent[0].x or lent[0][“x”] is the way to access