I am creating a little Shape class in javascript for canvas to kill some time. I was wondering if I could do something like below,
var Shape = function (shape) {
// pseudo code
if (shape is a prototype function of Shape) {
shape();
}
}
Shape.prototype.quad = function () {
}
So for the above the only valid string would be quad as that is the only prototypal function defined.
Is this possible?
Given that shape is a string, just use in to see if it exists on Shape.prototype
var Shape = function (shape) {
if (shape in Shape.prototype) {
Shape.prototype[shape]();
}
};
This of course doesn't give you a useful this value in Shape.prototype.quad, but I can't tell what you want there.
If you meant to do this as the constructor function, then you'd use this instead.
var Shape = function (shape) {
if (shape in this) {
this[shape]();
}
};
If you want also to make certain that it's a function, then use typeof.
if ((shape in this) && typeof this[shape] === "function") {
this[shape]();
}
Shape class that people can pass in a string and it would call the relative prototype function. So doing var shape = new Shape("quad"); would call the function to create a quadrilateral shape. Thank you again!I think what you are looking for is inheritance detection. This can be done by checking instanceof. Here is an example:
var Shape = function (shape) {
if( shape instanceof Shape ){
alert("shape instance found");
}
};
var Quad = function(){};
Quad.prototype = new Shape();
var q = new Quad();
var s = new Shape(q);
edit
Perhaps you would like to look for a prototype defined by a string? In that case, do this:
var Shape = function (shape) {
if( typeof this[shape] == "function" ){
alert("shape is a prototype function");
}
};
Shape.prototype.quad = function(){};
var c = new Shape("circle");
var q = new Shape("quad");
quad as that is the only prototypal function defined." differently.
eval("Shape.prototype."+shape) instanceof Shape? :-(false, since Shape.prototype.X is going to be a function (most likely) and not an instance of Shape. But instead of eval("Shape.prototype."+shape) you should use bracket notation: Shape.prototype[shape].Try this assuming Shape is a constructor, it uses the non-standard but commonly available proto property.
var Shape = function (shape) {
for (var functionName in this) {
if (this.__proto__.hasOwnProperty(functionName)) {
if (this[functionName] === shape) {
shape.call(this);
}
}
}
}
Shape.prototype.quad = function () { console.log("quad")}
new Shape(Shape.prototype.quad)
