キーダウンにバインドし、前後の値を比較して、サイズが縮小したかどうかを確認します。
$(input).keydown(function(){
var currVal = this.value, self = this;
setTimeout(function(){
if ( currVal.length > self.value.length ) {
console.log(currVal.length - self.value.length + " characters have been removed.");
}
},0);
});
http://jsfiddle.net/ymhjA/1/
更新されたサンプル:
$("input").keydown(function() {
var currVal = this.value,
self = this;
setTimeout(function() {
if (currVal.length - self.value.length === 1) {
var origVal = $.grep(currVal.split(""),function(val){
return val === " ";
});
var newVal = $.grep(self.value.split(""),function(val){
return val === " ";
});
if ( origVal.length != newVal.length ) {
console.log("a space was removed");
}
}
}, 0);
});
http://jsfiddle.net/ymhjA/4/