JavaScript with&eval妙用——根据表达式获取对象中对应的属性值

var getValue = (propExp,obj) => {

var result;

try {

var safeWindow = {

alert: noop,confirm: noop,prompt: noop

};

with (obj) {

result = eval.call(safeWindow,propExp);

}

} catch (error) {

}

return result;
}
var user = {

name: {

first: 'Jan',last: 'Toim'

},age: 20,address: [

{

address: '美国加州',phone: '333'

},{

address: '美国纽约',phone: '444'

}

]

};
getValue('age',user);//20

getValue('name',user);//{first: 'Jan',last: 'Toim'}

getValue('name',user)===user.name;//true

getValue('address[0].phone',user);//333

getValue('address[5].phone',user);//undefined

getValue('alert(22)',user);//undefined（不弹出alert）

 {
    var fun = new Function('obj','var noop = function () { };var result;try{var safeWindow={alert:noop,confirm:noop,prompt:noop};with(obj){result=' + propExp + '}}catch(error){};return result;');
    return fun(obj);
};