String to JavaScript array with elements as arrays

Since it's a valid JSON you can make it to number array by parsing it using JSON.parse method.

var string = "[[1,2],[3,4],[5,6],[7,8]]";
console.log(
 JSON.parse(string)
)

To convert to a string array you need to wrap number with " (quotes) to make string in JSON use String#replace method for that.

var string = "[[1,2],[3,4],[5,6],[7,8]]";
console.log(
 // get all number and wrap it with quotes("") 
 JSON.parse(string.replace(/\d+/g, '"$&"'))
)

From this answer https://stackoverflow.com/a/13272437/5349462 you should use

var array = JSON.parse(string);

JSON.parse() function can help you:

var string = "[[1,2],[3,4],[5,6],[7,8]]";
var array = JSON.parse(string);

JSON.parse() is supported by most modern web browsers (see: Browser-native JSON support (window.JSON))

You can use the below code to convert String to array using javascript. You simple use JSON.parse method to convert string to json object. As our specified string has two-dimensional array,we need to do operation on json object to get required format.

var string = "[[1,2],[3,4],[5,6],[7,8]]";
//parses a string as JSON 
var obj=JSON.parse(string);
console.log(obj);