Don't mutate passed-in props

[sophiebits]

Depends on #575; fixes #570. Now we'll be in trouble if someone tries to share objects between calls to getDefaultProps but that was already true of getInitialState and I haven't heard any complaints there.

This is the same number of allocations as before; we're just copying props in the other direction. (In any case, the copy happens only on mount and there are a couple dozen costlier things we're doing already at that time.)

[tommyh]

+1.

Can you explain what you mean by "we'll be in trouble if someone tries to share objects between calls to getDefaultProps but that was already true of getInitialState"? Like modifying a global object in the getDefaultProps or getInitialState? A few lines of pseudo code would help me understand this point. :)

[sophiebits]

Yep, if you do

var defaults = {banana: 17};
var Component = React.createClass({
    getDefaultProps: function() { return defaults; },
    // ...
});

then all components would share a .props object. Seems unlikely though.

[petehunt]

pulling this in

[paulshen]

did you mean to clone this._defaultProps here? this mutates the default prop object which gets reused on each pass.

[sophiebits]

In my original PR comment: "Now we'll be in trouble if someone tries to share objects between calls to getDefaultProps but that was already true of getInitialState and I haven't heard any complaints there."

But we can copy if that's a problem?

[paulshen]

MyComponent = React.createClass({
  getDefaultProps: function() { return {}; },
  render: function() { ... }
};

// render <MyComponent disabled={true} />
// update with <MyComponent />

we'll see that disabled is true for the second pass because this._defaultProps has been modified.

[sophiebits]

Ahh, you're right.