Dynamically assign element id inside ngFor

What you have is correct and should work in angular 4/5. Are you maybe using a really old, pre-release angular 2 version?

Here is a stackblitz with your code and the code below, both working

https://stackblitz.com/edit/angular-khur4v?file=app%2Fapp.component.html

You can also do it that way, which is the preferred way

<li *ngFor="let episode of episodes; let i = index">
    <div [attr.id]="'wave' + i">{{episode.name}}</div>
</li>

You can use {{ 'wave' + i }} instead of wave{{i}}. Make it as Angular Experession. This is the full ngFor:

<li *ngFor="let episode of episodes; let i = index">
     <div id="{{ 'wave' + i }}"></div>
</li>

It works and creates the div with the correct id

document.getElementById("wave1")

Output will be like this:

<div id=​"wave1">​wave1​</div>

but remember your code will start from wave0 as i = index starts from 0.

You don't need to define i

<li *ngFor="let episode of episodes">
    <div id="wave{{episode}}">{{episode}}</div>
</li>

EDIT: in case episodes is a list of objects

<li *ngFor="let episode of episodes">
    <div id="wave{{episodes.indexOf(episode)}}">{{episode.name}}</div>
</li>