The word joiner (WJ, U+2060) is a Unicode format character which is used to indicate that line breaking should not occur at its position. It does not affect the formation of ligatures or cursive joining and is ignored for the purpose of text segmentation.[1]
The word joiner replaces the zero-width no-break space (ZWNBSP, U+FEFF), as a non-breaking space of zero width. The ZWNBSP was originally and is currently used as the byte order mark (BOM) at the start of a file. However, if encountered elsewhere, it should, according to Unicode, be treated as a zero-width non-breaking space. The deliberate use of U+FEFF for this purpose is deprecated, with U+2060 strongly preferred.[1][2]