avoid errors if one of variable undefined all script stop working

my problem Confined to missing a value of a variables

users can put values of this vars

var name = "name";
var age = "age";
var sex = "sex";
var weight = "weight";

if one variable is not defined ,it make all script stop what's the best ways to avoid this error have atrying with

switch (variable){
default:
//codes
breake;
}

or

    switch (variable){
    case undefined:    //codes
    breake;
    }

or

if(typeof variable==='undefined'){
//do that
}

need to more Tips and Advice in this cases Especially if we have big code blocks ..please share your experience for intermediate learner