Part1

custom.js

registerBlockType('namespace/block-slug', {

//built-in attributes
title: 'The name',
description: 'Block to generate a custom event',
icon: 'format-image',
category: 'layout'

//custom attributes
attributes: {
	content: {type: 'string'}
},

//custom functions


//built-in functions
edit: function(props) {
    function somename(event) {
      props.setAttributes({content: event.target.value})
    }

    return wp.element.createElement(
      "div",
      null,
      wp.element.createElement(
        "h3",
        null,
        "Enter your sample text"
      ),
      wp.element.createElement("input", { type: "text", 
      	value: props.attributes.content, onChange: somename })
    );
  },

save() {}
});

you forget to put a comma after this line

category: 'layout'