ReactJS Warning: Thumbnails.shouldComponentUpdate(): Returned undefined instead of a boolean value. Make sure to return true or false

Question

I am doing a conditional in my shouldComponentUpdate method and if the condition matches return true, else return false... however I am still getting a "returned undefined instead of a boolean ..." as the title suggests.

Here is my method: * Note if I don't have the setTimeout it automatically assumes that nextProps.props.length is 0 even when its more than 0

shouldComponentUpdate(nextProps){
    setTimeout(()=>{
        console.log(nextProps.props, nextProps.props.length);
        if(nextProps.props.length > 0){
            return true;
        }else{
            return false;
        }
},1000)
}

it was returning as length 0 without the setTimeout regardless if the length was actually 0. Saw that in another solution. I figured it out though, I just had to use this.state in shouldcomponentupdate not this.props or nextProps ... So this question is solved ... now another problem though — moesh
– moesh, Commented Jul 27, 2017 at 13:15

Denialos · Accepted Answer · 2017-07-27 14:24:04Z

1

Your components props are actually stored in nextProps argument. It seems you're trying to access props in nextProps, which obviously looks fishy.

You should never name a prop of a component as generic as props, if that's really what you're trying to achieve. Give your component's props more descriptive names.

Also, the expression in shouldComponentUpdate can be simplified to:

shouldComponentUpdate(nextProps){
    return nextProps.props.length > 0; // assuming nextProps.props is an array
}

Additionally, you should post your component's propTypes definition, so the component's props contract is clear.

answered Jul 27, 2017 at 14:24

Denialos

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