1. bind value into 'this'

const area = function() {
    return this.width * this.height;
};
 
const boundArea = area.bind( { width: 2, height: 3 } );
boundArea();

2. format currency函数

const formatCurrency = function( 
    currencySymbol,
    decimalSeparator  ) {
    return function( value ) {
        const wholePart = Math.trunc( value / 100 );
        let fractionalPart = value % 100;
        if ( fractionalPart < 10 ) {
            fractionalPart = '0' + fractionalPart;
        }
        return `${currencySymbol}${wholePart}${decimalSeparator}${fractionalPart}`;
    }
}

getLabel = formatCurrency( '$', '.' );
getLabel(199)
getLabel(3005)