Multiple conditions in ngClass - Angular 4

You are trying to assign an array to ngClass, but the syntax for the array elements is wrong since you separate them with a || instead of a ,.

Try this:

<section [ngClass]="[menu1 ? 'class1' : '',  menu2 ? 'class1' : '', (something && (menu1 || menu2)) ? 'class2' : '']">

This other option should also work:

<section [ngClass.class1]="menu1 || menu2" [ngClass.class2] = "(menu1 || menu2) && something">    

you need object notation

<section [ngClass]="{'class1':condition1, 'class2': condition2, 'class3':condition3}" > 

ref: NgClass

There are multiple ways to write same logic. As it mentioned earlier, you can use object notation or simply expression. However, I think you should not that much logic in HTML. Hard to test and find issue. You can use a getter function to assign the class.

For Instance;

public getCustomCss() {
    //Logic here;
    if(this.x == this.y){
        return 'class1'
    }
    if(this.x == this.z){
        return 'class2'
    }
}
<!-- HTML -->
<div [ngClass]="getCustomCss()"> Some prop</div>

//OR

get customCss() {
    //Logic here;
    if(this.x == this.y){
        return 'class1'
    }
    if(this.x == this.z){
        return 'class2'
    }
}
<!-- HTML -->
<div [ngClass]="customCss"> Some prop</div>

<section [ngClass]="{'class1': expression1, 'class2': expression2, 
'class3': expression3}">

Don't forget to add single quotes around class names.