$(document).ready(function() {
    FunctionName();
});

$(document).ready(function() {
    FunctionName1();
});
$(document).ready(function() {
    FunctionName2();
});
$(document).ready(function() {
    FunctionName3();
});

_spBodyOnLoadFunctionNames.push("Init");

function Init() {
    Func1().done(function() {
        Func2().done(function() {
            Func3().done(function() {
                // All three functions with asynchronous calls now completed in order successfully
            });
        });
    });
}

function Func1() {
    var dfd = $.Deferred();
    $.ajax({
        url: //url,
        type: "GET",
        headers: {
            "accept": "application/json;odata=verbose",
        },
        success: function (data) {
            // Do something with data if you want to
            dfd.resolve();
        },
        error: function (data) {
            // Do something with data if you want to
            dfd.reject();
        }
    });
    return dfd;
}

function Func2() {
    // Exactly as Func 1
}

function Func3() {
    // Exactly as Func1
}

function Init() {
    $.when(Func1(), Func2()).done(function() {
        Func3();
    });
}

function Init() {
    Func1();
    Func2();
    Func3();
}

SP.SOD.executeFunc('sp.js', 'SP.ClientContext', readyFunction);

function readyFunction() {
    Function1();
    Function2();
    Function3();
}

$(function(){
function1();
function2();
function3();
});

$(function(){
...
});

$(function(){
function1();
});

$(function(){
function2();
{);