How to convert a Request XMLHttpRequest [duplicate]

Good afternoon.

I am querying a file of type Json, when I make the request it returns in a String format, such as to make it come in a JSON format to be manipulative.

reqListener() {

    return new Promise((resolve, reject) => {

        // function reqListener() {
        //     console.log(this.responseText);
        // };

        let oReq = new XMLHttpRequest();

        oReq.onload = () => {

            if (oReq.readyState == 4) {

                if (oReq.status == 200) {
                    resolve(oReq.responseText);
                }

            } else {

                reject("erro ao conectar");

            }
        };

        oReq.open("get", "list.json", true);
        oReq.send();

    })

}

Json:

{
"cliente": [
    {
        "nome": "Rumble",
        "peso": 50,
        "altura": 1.40
    },
    {
        "nome": "Ana",
        "peso": 70,
        "altura": 1.80
    },
    {
        "nome": "Jose",
        "peso": 90,
        "altura": 1.30
    },
    {
        "nome": "Jose",
        "peso": 90,
        "altura": 1.30
    },
    {
        "nome": "Jose",
        "peso": 90,
        "altura": 1.30
    }
]
}