JSFiddle - React, Tailwind, and code Playground

HTML

<textarea id="xxx">
    11111111
    222222222
</textarea>    
<button id="yyy">Вставить</button>

JavaScript

$.fn.extend({
    insertAtCaret: function(myValue) {
        if (document.selection) {
                this.focus();
                sel = document.selection.createRange();
                sel.text = myValue;
                this.focus();
        }
        else if (this.selectionStart || this.selectionStart == '0') {
            var startPos = this.selectionStart;
            var endPos = this.selectionEnd;
            var scrollTop = this.scrollTop;
            this.value = this.value.substring(0, startPos)+myValue+this.value.substring(endPos,this.value.length);
            this.focus();
            this.selectionStart = startPos + myValue.length;
            this.selectionEnd = startPos + myValue.length;
            this.scrollTop = scrollTop;
        } else {
            this.value += myValue;
            this.focus();
        }
    }
})
$('#yyy').click(function(){
    $('#xxx').insertAtCaret('-TEXT-');
});