tinymce.js 4.9.10
так не получилось placeholder: "Ask a question or post an update...",
wp.editor.initialize(
editor_id,
{
tinymce: {
wpautop: true,
placeholder: "Ask a question or post an update...",
plugins : 'charmap colorpicker compat3x directionality hr image lists media paste tabfocus textcolor wordpress wpautoresize wpdialogs wpeditimage wpemoji wpgallery wplink wptextpattern wpview',
toolbar1: 'bold italic underline strikethrough | link unlink | fullscreen |formatselect forecolor | image',
},
mediaButtons: true,
}
);