JSFiddle - React, Tailwind, and code Playground

JavaScript

var data = [{ name: 'bart' }, { name: 'baz' }];

    function getPropIndexByName(data, prop, str){

        var ret = []; //updated to handle multiple indexes

        $.each(data, function(k, v){
            if(v[prop] === str)
                ret.push(k);
        });
        
        return ret;
    }

    console.log(getPropIndexByName(data, 'name', 'bart'));