React warning: Functions are not valid as a React child

Question

I have this react component. This is not rendering properly but getting an annoying warning like

Functions are not valid as a React child. This may happen if you return a Component instead of from the render. Or maybe you meant to call this function rather than return it.

Here's my component. What am I doing wrong here?

import React, { Component } from 'react';

class Squares extends Component {   

    constructor(props){
        super(props);
        this.createSquare = this.createSquare.bind(this);
    }

    createSquare() {
        let indents = [], rows = this.props.rows, cols = this.props.cols;
        let squareSize = 50;
        for (let i = 0; i < rows; i++) {
            for (let j = 0; i < cols; j++) {
                let topPosition = j * squareSize;
                let leftPosition = i * squareSize;
                let divStyle = {
                    top: topPosition+'px', 
                    left: leftPosition+'px'
                };
                indents.push(<div style={divStyle}></div>);
            }   
          }
        return indents;
    }    

    render() {
      return (
        <div>
            {this.createSquare()}
        </div>
      );
    }
}

export default Squares;

UPDATE

@Ross Allen - After making that change, the render method seems to be in infinite loop with potential memory crash

Answer 1

You need to call createSquare, right now you're just passing a reference to the function. Add parentheses after it:

render() {
  return (
    <div>
      {this.createSquare()}
    </div>
  );
}