Reference · Strings

cursor_index

cursor_index(str, int) -> int

What it does

The place in s, in characters, of a field's cursor at n: a field's selectionStart counts UTF-16 units, as JavaScript does, and slice, len and s[i] count characters. Past an emoji or another character outside the first plane the two differ, and this turns the one into the other. The same on the server and in the browser.

Examples

print(cursor_index("héllo", 3), cursor_index("😀 hi", 2), cursor_index("😀 hi", 3))print(slice("😀 hi", cursor_index("😀 hi", 3)))

3 1 2hi

component Mention() {    state text = ""    <textarea @input={(e) => {        text = e.value        let at = cursor_index(text, e.target.selectionStart)        let before = slice(text, 0, at)    }}/>}

Edge cases

• Below 0 is 0, and past the end is the text's length.
• A cursor between the two halves of an emoji counts that emoji.

print(cursor_index("abc", 0), cursor_index("abc", 9), cursor_index("abc", -2), cursor_index("", 4), cursor_index("😀", 1))

0 3 0 0 1

Errors

Text and an int, or it is a runtime error.

print(cursor_index(5, 1))

line 1: `cursor_index` expects a str as argument 1

Chaining

text | cursor_index(n) is cursor_index(text, n).

See also

slice, len

Edit this page on GitHub · every example's output was made by running it (tools/refcheck.mjs) · questions on Discord or r/quillo