JavaScript Scope Using let in loops instead of var (click handlers example)
Example
Let's say we need to add a button for each piece of loadedData array (for instance, each button should be a slider showing the data; for the sake of simplicity, we'll just alert a message). One may try something like this:
for(var i = 0; i < loadedData.length; i++)
jQuery("#container").append("<a class='button'>"+loadedData[i].label+"</a>")
.children().last() // now let's attach a handler to the button which is a child
.on("click",function() { alert(loadedData[i].content); });
But instead of alerting, each button will cause the
TypeError: loadedData[i] is undefined
error. This is because the scope of i is the global scope (or a function scope) and after the loop, i == 3. What we need is not to "remember the state of i". This can be done using let:
for(let i = 0; i < loadedData.length; i++)
jQuery("#container").append("<a class='button'>"+loadedData[i].label+"</a>")
.children().last() // now let's attach a handler to the button which is a child
.on("click",function() { alert(loadedData[i].content); });
An example of loadedData to be tested with this code:
var loadedData = [
{ label:"apple", content:"green and round" },
{ label:"blackberry", content:"small black or blue" },
{ label:"pineapple", content:"weird stuff.. difficult to explain the shape" }
];
