JavaScript question, rewrite the function to add infinitely_javascript skills

function add(x) {_______}; alert(add(2)(3)(4)); //Fill in the blanks so that the result is 9
Solution 1,

Copy code The code is as follows:

//貘大
function add(x) {
var c = 0;
return function(x) {
c = c x ; arguments.callee.toString = function(){
return c;
};
return arguments.callee;
}(x);
};
alert(add(2)(3)(4));

Solution 2,

Copy code The code is as follows:

//Sangui
function add(x) {
return function(y){
return function(z ){
return x y z;
}
}
};
alert(add(2)(3)(4));

Solution 3,

Copy code The code is as follows:

//Situ Zhengmei
function add (a) {
if(!isFinite(add.i)){
add.i = a
}else {
add.i = a;
}
add.valueOf = add .toString = function(){
return add.i
}
return add;
}
alert(add(2)(3)(4))

Actually, the above question is a curry test. Please see my other blog post for details.
If you have a different solution, please give me some advice!