Check whether a node is editable or not in TypeScript

isEditable.ts

/**
 * Checks whether the passed in node is editable or not.
 * An editable node is one that returns true to isContentEditable or has a tag name as
 * any one of the following:
 * "textarea", "input", "text", "email", "number", "search", "tel", "url", "password"
 *
 * @param node the node to check
 * @return true if the node is editable and false otherwise
 */
function isEditable(node: Node): boolean {
    let element = node as HTMLElement;
    let nodeName: string = element.nodeName.toLowerCase();

    let editables = ["textarea", "input", "text", "email", "number", "search", "tel", "url", "password"];

    return (element.isContentEditable || (element.nodeType === Node.ELEMENT_NODE && editables.contains(nodeName)));
}