Accessing or creating nested JavaScript objects with string key without eval

Question

I am looking for a nice solution to access a property by string value, but if the property does not exist it should create it. If the root structure already has defined some parts of the structure, the attributes should not be overwritten, but merged instead.

For example if you have an empty object

test

and you want to set a deep structure without using eval. e.g.

test = {}

test.foo.name = "Hallo" // <<- foo is an Object

test.foo[3] = "Test" // <<- foo should remain as Object, not as Array 

test.foo.data[3].bar = 100 // <<- should not overwrite test.foo.name

I have written a solution that actually works, but it is quite bad code, I guess:

Also available as jsfiddle: https://jsfiddle.net/gvaLzqqf/4/

Object.setValue = function(node, flatKey, value) {

    flatKey = flatKey.replace("[", ".");

    flatKey = flatKey.replace("]", "");

    var parts = flatKey.split(".")

    var oldNode = node

    parts.forEach(function(key, index) {

      if (/^\+?(0|[1-9]\d*)$/.test(key)) {

        key = key * 1

        if (index > 0) {

          var oldValue = parts[index - 1]

          if (!Array.isArray(oldNode[oldValue])) {

            oldNode[oldValue] = []

            node = oldNode[oldValue]

          }

        }

      }

      if (node[key] == undefined) {

        node[key] = {}

      }

      oldNode = node

      node = node[key]

    }); // for each

    oldNode[parts[parts.length - 1]] = value

    return oldNode[parts[parts.length - 1]]

  } // function



var test = {}

Object.setValue(test, "foo.name", "Mr. Foo")

Object.setValue(test, "foo.data[0].bar", 100)

Object.setValue(test, "and.another[2].deep", 20)



console.log("test = " + JSON.stringify(test))

console.log("test.foo.data[0].bar = " + test.foo.data[0].bar)

How ever, is there any better way to achieve this?

Answer 1

You could split the path and reduce the path by walking the given object. If no Object exist, create a new property with the name, or an array. Later assign the value.

function setValue(object, path, value) {
    var way = path.replace(/\[/g, '.').replace(/\]/g, '').split('.'),
        last = way.pop();

    way.reduce(function (o, k, i, kk) {
        return o[k] = o[k] || (isFinite(i + 1 in kk ? kk[i + 1] : last) ? [] : {});
    }, object)[last] = value;
}

var test = {};
setValue(test, "foo.name", "Mr. Foo");
setValue(test, "foo.data[0].bar", 100);
setValue(test, "and.another[2].deep", 20);
console.log(test);

Accessing or creating nested JavaScript objects with string key without eval

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