a.js

var data = [1, 4, 5, 6, 7, 8];
//var data = [2, 3, 5, 7, 11, 13, 17];
//var data = [2, 3, 5, 10, 20];
var a = [];

var r = function(u) {
    if(a.length == data.length - 1) {
        if(u) return solve();
        else return false;
    }
    if(!u) {
        a.push("=");
        r(true);
        a.pop();
    }
    a.push("+"); r(u); a.pop();
    a.push("-"); r(u); a.pop();
    a.push("*"); r(u); a.pop();
};
var solve = function() {
    var ret = ["" + data[0], ""];
    var index = 0;
    for(var i = 0; i < a.length; i++) {
        if(a[i] == "=") { index++; ret[index] = data[i + 1]; }
        else ret[index] += a[i] + data[i + 1];
    }
    if(eval(ret[0]) == eval(ret[1])) {
        console.log(ret.join("="));
    }
};
r(false);