Converts JSON to an HTML string. JSON is assumed to already be HTML-Escaped.

jtoh.js

//
// Author: Dean Bassett
//
// Converts JSON to an HTML string. JSON is assumed to already be HTML-Escaped.
// The name for function is inspired by the C function `atoi`.
//
// this converter takes an object with 3 attributes:
//    tag (string, required):   the html tag
//    attributes (object):      key-value pairs which represent the attributes for the tag
//    content (many types)...
//          (string): Represents a text node
//          (object): Represents an HTML node, with fields as defined above
//          (array):  Represents many nodes, either type string or object
//
function jtoh(js) {
    let contentStr = "";

    function addContent(content) {
        if (typeof content === "string" || typeof content === "number") {
            contentStr += content+"";
        } else if (typeof content === "object" && content !== null) {
            contentStr += jtoh(content)
        } else {
            throw Error("Invalid content: " + content + " (type " + (typeof content) + ")");
        }
    }

    // Calculate content
    if (js.content === undefined) {
        // let content be empty if not defined
    } else if (Array.isArray(js.content)) {
        for (let i = 0; i < js.content.length; i++) {
            addContent(js.content[i]);
        }
    } else {
        addContent(js.content);
    }

    // Calculate attributes
    let attribStr = "";

    if (js.attributes === undefined) {
        // let attributes be empty if not defined
    } else if (typeof js.attributes === "object" && js.attributes !== null) {
        for (let k in js.attributes) {
            let v = js.attributes[k];
            if (typeof v !== "string" || typeof k !== "string") {
                throw Error("Invalid attribute " + k + " :: " + v + " (types " + (typeof k) + " :: " + (typeof v) + ")");
            }
            attribStr += `${k}="${v}"`
        }
    } else {
        throw Error("Invalid attributes object: " + js.attributes + " (type " + (typeof js.attributes) + ")");
    }

    // Tag
    if (typeof js.tag === "string") {
        if (contentStr !== "") {
            return `<${js.tag} ${attribStr}>${contentStr}</${js.tag}>`;
        }
        switch (js.tag) {
            case "area":
            case "base":
            case "br":
            case "col":
            case "embed":
            case "hr":
            case "img":
            case "input":
            case "keygen":
            case "link":
            case "meta":
            case "param":
            case "source":
            case "track":
            case "wbr":
                return `<${js.tag} ${attribStr}>`;
            default:
            return `<${js.tag} ${attribStr}>${contentStr}</${js.tag}>`;
        }
    } else {
        throw Error("Invalid tag " + js.tag + " (type " + (typeof js.tag) + ")");
    }
}

Updated to fix a bug with self-closing tags