If a=[[1,[],"f",3],[3,[4,"x"]]] and b=[1,1].
I want to read a by b like a[1][1] to get [4,"x"]. Note that b is an array which should only consist of integers.
You could also do eval('a['+b.join('],[')+']') but requires the actual variable name as string and it's ugly.
Here are some of my functions:
Array.prototype.readByArray = function(a) {
var c = this;
for (var i = 0; i < a.length; i++) {
c = c[a[i]];
}
return c;
};
Array.prototype.emptyByArray = function(a) {
var c = this.readByArray(a);
c.splice(0, c.length);
};
Array.prototype.concateByArray = function(a, e) {
var c = this.readByArray(a);
for (var i = 0; i < e.length; i++) {
c.push(e[i]);
}
};
Array.prototype.setByArray = function(a, e) {
this.emptyByArray(a);
this.readByArray(a).push(e);
};
This could be useful for reading a nested array in an imperative way in this example:
Array.prototype.readByArray=function(a){var c=this;for(var i=0;i<a.length;i++){c=c[a[i]];}return c;};
var a = [1,2,3,[1,2,3,[{x: 3},"test"],4],"foo","bar"]; //Your array
var b = [0]; //Reading stack
var s = '[\n'; //Output
while(b[0]<a.length){
if(Array.isArray(a.readByArray(b))){
s+=' '.repeat(b.length)+'[\n';
b.push(-1);
}else{
s+=' '.repeat(b.length)+JSON.stringify(a.readByArray(b))+'\n';
}
b[b.length-1]++;
while(b[b.length-1]>=a.readByArray(b.slice(0,-1)).length){
b.pop();
b[b.length-1]++;
s+=' '.repeat(b.length)+']\n';
}
}
console.log(s);
Is there any better way to do this? Are there native functions for this?
2 Answers 2
You could use Array#reduce for it.
You start with the whole array and return for every element of b a part of the array until all indices are used.
var a = [[1, [], "f", 3], [3, [4, "x"]]],
b = [1, 1],
result = b.reduce(function (v, i) {
return v[i];
}, a);
console.log(result);ES6
var a = [[1, [], "f", 3], [3, [4, "x"]]],
b = [1, 1],
result = b.reduce((v, i) => v[i], a);
console.log(result);
result[0] = 42;
console.log(a);
result.splice(0, result.length, 'test');
console.log(a);.as-console-wrapper { max-height: 100% !important; top: 0; }5 Comments
const result = b.reduce((v, i) => v[i], a)[4,"x"]?result=["test"] how would I do that?Array#splice, for keeping the reference and delete all elements inside and move the new content to the reference. please see edit in the second example.I had written a reusable generic code exactly for this purpose to get the nested object properties dynamically. Actually i was targeting objects but since in JS an array is a perfect object it also applies for arrays too. So lets see how it works in this particular case;
Object.prototype.getNestedValue = function(...a) {
return a.length > 1 ? (this[a[0]] !== void 0 && this[a[0]].getNestedValue(...a.slice(1))) : this[a[0]];
};
var a = [[1,[],"f",3],[3,[4,"x"]]],
b = [1,1],
c = a.getNestedValue(...b);
console.log(c)
Array's prototype. It will give you more headaches than usefulness.