React not rendering component

Question

This is my code:

var Item = React.createClass({
    render: function () {
        return (
                React.createElement('div', {},
                        React.createElement('span', {}, this.props.a),
                        React.createElement('span', {}, this.props.b)
                        )
                );
    }
});

var RParent = React.createClass({
    getInitialState: function () {
        return {messages: []};
    },
    addMess: function (data) {
        var self = this;
        self.state.messages.push({
            a: data.a,
            b: data.b
        });
        this.setState({messages: self.state.messages});
    },
    render: function () {
        var messages = this.state.messages;
        return (
                React.createElement('div', {},
                        React.createElement(Item, messages))
                );
    }
});

var box = ReactDOM.render(React.createElement(RParent), document.getElementById('parentDiv'));

function render(a, b) {
    box.addMess({
        a: a,
        b: b
    });
}

Data is sent to the render function. It appears that somehow the properties are not reaching the render function of the Item as they appear to be undefined when I try print them to console.

Any ideas why this might be happening?

The problem is that nothing is rendered into the "parentDiv". It just remains blank. However, on inspecting the elements, I can still see two "span" children under it (which were not created in html or anywhere else except here). But those span elements have no content.

Amoolya S Kumar · Accepted Answer · 2016-12-01 07:02:11Z

1

I think there's a fundamental problem to your code. You are trying to pass 'a' and 'b' to your react component through an external function 'render' that seems to be invoking one of the component's functions. This is wrong.

You should pass 'a' and 'b' to your React component RParent as props. Whenever the value of 'a' and 'b' change, your parent component will automatically rerender.

var Item = React.createClass({
render: function () {
    return (
            React.createElement('div', {},
                    React.createElement('span', {}, this.props.a),
                    React.createElement('span', {}, this.props.b)
                    )
            );
}
});

var RParent = React.createClass({
getInitialState: function () {
    return {messages: []};
},
,
render: function () {
    var messages = this.props.messages;
    return (
            React.createElement('div', {},
                    React.createElement(Item, messages))
            );
}
});

ReactDOM.render(
    (<RParent messages= {'a': a, 'b': b} />)
    , document.getElementById('parentDiv'));

edited Dec 1, 2016 at 7:02

answered Dec 1, 2016 at 6:56

Amoolya S Kumar

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5 Comments

yadhu Over a year ago

<RParent messages= {'a': a, 'b': b} /> what are a and b that you're assigning to the keys?

Amoolya S Kumar Over a year ago

@free-soul I deleted the other answer. a and b are the values, same as in the question. Please see the render function.

user3271166 Over a year ago

@AmoolyaSKumar Thanks, just a quick question, I haven't tried the code yet (won't be able to for a while) but may I ask where should I be pushing element into messages array? In render event? Or componentWillMount event? My implementation demands array for the control so I need to have an array too

Amoolya S Kumar Over a year ago

Hey, I will need to see your entire code to tell you exactly. Basic rules are : 1: you cannot change a component's props from within a component. (If you want RParent component to push elements into messages array, you should keep it in the state, and not props.) 2: You can change the component's state in any lifecycle method (componentDidReceiveProps or componentDidMount), (but NOT in render method)

user3271166 Over a year ago

Thanks, that helped!

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