error about endswith() method second param

[JansenZ]

MDN say If provided overwrites the considered length of the string to search in. If omitted, the default value is the length of the string.

var str = 'To be, or not to be, that is the question.';

console.log(str.endsWith('question.')); // true
console.log(str.endsWith('to be'));     // false
console.log(str.endsWith('to be', 19)); // true

which means

console.log(msg.endsWith("o", 8));          // true

this o is not o in 'hello'; this o is o in 'world';

[sudarsangp]

Yes you are right, when the example is changed to

var message = "hellm world";
message.endsWith('o', 8); // prints true in console

[chaoobject001]

On page 20: "endsWith() starts the match from the length of the string minus the second argument" This statement may be contradicting https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/endsWith and what I observed in browser console

What I observed is that: given second argument is provided as X, when user invokes endsWith() Then the sub-string to be searched start from index 0 to index {X}

Example: let msg = "012345678"; console.log(msg.endsWith("23", 4)); // true

[nzakas]

Thanks, that’s definitely a mistake. I’ll get that fixed.

[ronen-e]

With regards to the comment from @chaoobject001 :

What I observed is that: given second argument is provided as X, when user invokes endsWith() Then the sub-string to be searched start from index 0 to index {X}

Example: let msg = "012345678"; console.log(msg.endsWith("23", 4)); // true

That is not correct according to the specs: https://www.ecma-international.org/ecma-262/10.0/index.html#sec-string.prototype.endswith

String.prototype.endsWith ( searchString [ , endPosition ] )

and also conflicts with the information found in https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/endsWith

1. The length (len) of the string to work on is treated as the second argument.
   If it is omitted then len = msg.length Note: if endPosition is greater then msg.length then msg.length is used for len

2. The start position to search from is: len - searchString.length

3. The search is made from len - searchString.length to len

Needs fix

So the text in the book is contradictory to the specs:

In chapter 2 under "Methods for Identifying Substrings"

When the second argument is provided, includes() and startsWith() start the match from that index while endsWith() starts the match from the second argument;

Suggested text

"while endsWith() starts the match from the second argument, or if omitted, from the length of the string, minus the length of the first argument"

In chapter 2 under "Methods for Identifying Substrings"

The call to msg.endsWith("o", 8) starts the search from index 0 and searches up to index 7, which is the "o" in "world".

Suggested text

The call to msg.endsWith("o", 8) starts the search from index 7 (inclusive) and searches up to index 8 (exclusive), which is the "o" in "world"