JSFiddle - React, Tailwind, and code Playground

HTML

<textarea rows="10" cols="50" id="textarea">   
John: 2

Jane: 3

John: 4

Jane: 5 
</textarea>

JavaScript

var result = {};
document.getElementById('textarea').value.match(/\w+:\s+\d+/g)
.forEach(function(element) {
    var data = element.match(/(\w+):\s+(\d+)/),
        name = data[1],
        value = data[2];
    if (typeof result[name] == 'undefined') {
        result[name] = 0;
    }
    result[name] += +value;
});
console.log(result);